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Salt crystals are formed when saline water evaporates. During this process, small parts of the brine become trapped in the salt and end up as fluid inclusions. Any halophilic microorganisms present in the fluid will be trapped as well. Large, ancient deep deposits of salt exist all over our planet. For instance, there are extensive salt deposits deep under Germany, Denmark and the North Sea, formed million years ago from shallow seas which evaporated when the climate in Europe was much warmer because of an equatorial position of the European continent caused by plate tectonics.
Similar formations are found elsewhere on the planet. When ancient fluid inclusions from such deposits are opened and the fluid is transferred to culture media for halophiles, growth occurs and the growing organisms exhibit a large species diversity [ 36 ]. It seems very probable that these growing halophiles were captured million years ago during the formation of the salt deposits.
This finding invokes many intriguing questions, regarding how long microorganisms can survive and specifically, how halophiles could stay alive for million years in their small, saline prisons. These observations do indeed imply that some microorganisms may have eternal life, at least in relation to the brief lifetime of most plants and animals.
Igneous rocks are the predominant solid constituents of the earth, formed through cooling of molten or partly molten material at or beneath the earth's surface. These rocks are penetrated by humans for a variety of purposes such as mining for metals, the extraction of groundwater and the building of tunnels and vaults for communication, transport, defence, storage, deposition and waste disposal. The concept of underground storage of hazardous wastes is commonly applied to materials that are impossible to transform to a non-hazardous form.
One group of such materials is the toxic metals, especially heavy metals and radionuclides. The disposal concepts vary from country to country, but igneous rocks are commonly in target for countries with access to these types of geological structures. Deposition of long-lived hazardous wastes requires extremely good knowledge about the igneous rock environment to be used as a host. Particularly the nuclear waste industry invests large sums in research on the safe underground disposal of all types of radioactive wastes [ 37 ].
Early studies in the Swedish long-term nuclear waste disposal research programme on subterranean microbiology revealed previously unknown microbial ecosystems in igneous rock aquifers at depths exceeding m [ 38 ]. This discovery triggered a thorough exploration of the subterranean biosphere in the aquifers of the Fennoscandian Baltic Shield [ 39 ].
Similarly, the Canadian radioactive waste disposal programme has stimulated investigations of microorganisms in deep igneous rock aquifers of the Canadian Shield [ 40 ]. Other investigations examined the potential risk of radionuclide migration caused by microorganisms able to survive in the deep groundwater systems [ 41 ].
It soon became apparent that microbial communities exist in most, if not all, deep aquifers [ 38 ]. Attention was then shifted to assay the activity potential of these microorganisms using radiotracer methods [ 42—45 ]. This work has also revealed several hitherto unknown microbial species adapted to life in igneous rock aquifers [ 48—50 ]. The repeated observations of autotrophic, hydrogen-dependent microorganisms in the deep aquifers imply that hydrogen may be an important electron and energy source and carbon dioxide an important carbon source in deep subsurface ecosystems.
Therefore, a model has been proposed of a hydrogen-driven biosphere in deep igneous rock aquifers in the Fennoscandian Shield [ 39 ]. A similar model has been suggested for deep basalt aquifers [ 52 ].
The organisms at the base of these ecosystems are assumed to be autotrophic acetogens capable of reacting hydrogen with carbon dioxide to produce acetate, autotrophic methanogens that produce methane from hydrogen and carbon dioxide, and acetoclastic methanogens that produce methane from the acetate product of the autotrophic acetogens Fig. All components needed for the life cycle in Fig. Consequently, the model is supported by the qualitative data obtained so far. Ideally, the next step will be to obtain quantitative data, which would require very sensitive experimental conditions, because of the very slow metabolic rates that are expected under non-disturbed conditions.
The central question in such an experimental endeavour is whether or not in situ hydrogen-driven microbial chemolithoautotrophic activities at depth are in balance with estimated renewal rates of hydrogen. An indisputable positive answer to this question is crucial for the unequivocal confirmation of a deep hydrogen-driven biosphere. The deep hydrogen-driven biosphere hypothesis, illustrated by its carbon cycle. At relevant temperature and water availability conditions, intraterrestrial microorganisms are capable of performing a life cycle that is independent of sun-driven ecosystems.
Hydrogen and carbon dioxide from the deep crust of the earth are used as energy and carbon sources. Caves may provide the link between surface and subsurface environments. The cave environment varies tremendously. This cave is therefore a good example of an intraterrestrial cave environment. Allochthonous organic input to the cave is limited due to the depth, but bacterial and fungal colonisation is relatively extensive [ 53 ]. Various points of evidence suggest that autotrophic bacteria are present in the ceiling-bound residues and could act as primary producers in a unique subterranean microbial food chain.
Because other major sources of organic matter have not been detected, it is suggested that these bacteria provide requisite organic matter to the known heterotrophic bacteria and fungi in the residues. The cave-wide bacterial and fungal distribution, the large volumes of corrosion residues and the presence of ancient bacterial filaments in unusual calcite speleothems biothems attest to the apparent longevity of microbial occupation in this cave.
More research should be invested in this and other caves to reveal the ecology and the biogeochemistry of cave ecosystems. The search for the maximum depths for life in various intraterrestrial environments will probably always be one major desire in the exploration of deep life.
Knowing more about these limits to life within our planet will enable more precise calculations of the total amount of intraterrestrial organisms. Therefore, these deep crustal environments are relevant targets for the search of the maximum temperature for life. A paper on anaerobic degradation and methane production from long chain alkanes by a consortium of microorganisms was recently published [ 54 ]. A team of seven different microorganisms were observed to crack the hydrocarbon, to produce methane and carbon dioxide and also to expel hydrogen sulfide.
This is an encouraging result for those who believe that any catabolic reaction that can be linked to oxygen as the electron acceptor, may also occur in the absence of oxygen, albeit slower and as a result of collaboration between species. The experiment showing anaerobic degradation of alkanes continued for almost two years before conclusive results were obtained.
One implication deduced from these results is that intraterrestrial microbes play in a very different league from those in well-fed, aerobic, pure cultures. Patience, a great deal of time and advanced culturing methods will be required for successful exploration of the metabolic activities of intraterrestrial microbial communities. Most deep environments contain methane in varying concentrations. Methane oxidation in aerobic environments is well documented and very widespread on the planet. As yet, there exists no microorganism, or community of microorganisms, in culture that oxidises methane under anaerobic conditions, although much indirect evidence for the occurrence of this process in nature has been published see, e.
If a metabolic process for anaerobic methane oxidation can be demonstrated, then a tremendous source of energy and carbon will become available for models of how intraterrestrial life is fuelled. The theory of a deep biosphere driven by hydrogen generated in deep geological strata Fig. There are at least six possible processes whereby crustal hydrogen is generated [ 56 ]:. The reaction between dissolved gases in the carbon—hydrogen—oxygen—sulfur system in magmas, especially in those with basaltic affinities. Radiolysis of water by radioactive isotopes of uranium and thorium and their daughter isotopes, and potassium.
It is important to explore the scale of these processes and the rates at which the produced hydrogen is becoming available for deep microbial ecosystems. The idea, in conclusion, that life originated on the surface of our planet, where it was strongly dependent on a hypothetical primordial soup, has recently come up against strong competition. Today there are several suggestions that life originated in the form of a thermophilic lithotroph [ 57 ] and that the birthplace was intraterrestrial, perhaps a hydrothermal vent area [ 58 ].
Consequently it should be obvious that the search for extraterrestrial life should concentrate on samples from under the surface of other planets [ 59 ]. However, that is another topic and far too speculative for this mini-review. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Close mobile search navigation Article navigation. Exploration of deep intraterrestrial microbial life: Abstract Intraterrestrial life has been found at depths of several thousand metres in deep sub-sea floor sediments and in the basement crust beneath the sediments.
Autotrophy , Biosphere , Groundwater , Rock , Subsurface. View large Download slide. Search for hyperhermophilic microorganisms in fluids obtained from the KTB pump test. Thermophilic, anaerobic bacteria isolated from a deep borehole in granite in Sweden. Thermodesulforhabdus norvegicus gen, sp. Organic carbon content, bacterial methanogenesis, and accumulation processes of gas hydrates in marine sediments. Alteration of oceanic volcanic glass: Deep marine biosphere fuelled by increasing organic matter availability during burial and heating.
Textural and chemical effects of bacterial activity on basaltic glass: Archaeoglobus fulgidus isolated from hot north sea oil field waters. Post-sampling changes in microbial community composition and activity in a subsurface paleosol. Observations pertaining to the origin and ecology of microorganisms recovered from the deep subsurface of Taylorsville Basin, Virginia.
A molecular comparison of culturable aerobic heterotrophic bacteria and 16S rDNA clones derived from a deep subsurface sediment. Towards complete biodiversity assessment: Pore-size constraints on the activity and survival of subsurface bacteria in a late Cretaceous shale-sandstone sequence, northwestern New Mexico. Distribution and diversity of halophilitic bacteria in a subsurface salt formation. Distribution and activity of bacteria in deep granitic groundwaters of southeastern Sweden.
The Canadian approach to microbial studies in nuclear waste management and disposal. Incorporation of CO 2 and introduced organic compounds by bacterial populations in groundwater from the deep crystalline bedrock of the Stripa mine. Assimilation of CO 2 and introduced organic compounds by bacterial communities in ground water from Southeastern Sweden deep crystalline bedrock. Carbon transformations by attached bacterial populations in granitic groundwater from deep crystalline bed-rock of the Stripa research mine.
Characterization of attached bacterial populations in deep granitic groundwater from the Stripa research mine with 16S-rRNA gene sequencing technique and scanning electron microscopy. Investigation of the potential for microbial contamination of deep granitic aquifers during drilling using 16S rRNA gene sequencing and culturing methods. Methylomonas scandinavica , sp. Diversity and activity of microorganisms in deep igneous rock aquifers of the Baltic Shield.
Energy gases of abiogenic origin in the Earth's crust. The future of energy gases. Activated actic acid by carbon fixation on Fe, Ni S under primordial conditions. The emergence of life from iron monosulphide bubbles at a submarine hydrothermal redox and pH front. Search for past life on Mars: Email alerts New issue alert. In progress issue alert. Receive exclusive offers and updates from Oxford Academic. More on this topic Denitrifying haloarchaea: Mutagenesis and expression of methane monooxygenase to alter regioselectivity with aromatic substrates. Accelerated methanogenesis from aliphatic and aromatic hydrocarbons under iron- and sulfate-reducing conditions.
Hydrocarbon uptake by Streptomyces. Related articles in Web of Science Google Scholar. Most youth also experience violence through media, including television, movies and video games. For instance, the average year old observes approximately 6, acts of violence on television and in movies in one year Browne and Hamilton-Giachritsis ; Center for Research Excellence Although exposure to violence is a cause for concern across all stages of youth development, this study focuses on late adolescents and emerging adults ages and their exposure to violence in the community and passive media television and movies.
This age group may be at a greater risk for the negative effects of exposure to these types of violence than younger youth, because they are more likely to experience community violence and more severe types of real-life violence e. In addition, older youth spend more time watching movies and television overall and the programs they watch are substantially more violent than those watched by younger adolescents Center for Research Excellence Although more mature than younger youth, older adolescents and emerging adults are still vulnerable to negative influences such as exposure to violence due to ongoing developmental processes e.
The negative influences of exposure to violence on youth have been widely studied. In particular, there is evidence that exposure to both real-life and media violence increases aggressive and antisocial behavior Bushman and Huesmann ; Huesmann et al. However, it should be noted that the causal role of media violence in aggression remains controversial, as some studies suggest that the effects of media violence are often inflated by methodological problems, such as poor measurement and failure to control for confounding variables, and that the effects on actual aggressive and violent behavior are too small to be of practical significance Ferguson and Kilburn ; Savage and Yancey Accordingly, when exposures to media and community violence were compared in a single study of older adolescents, violence in the community was more strongly related to aggression than violent media Boxer et al.
Nevertheless, both types of exposure to violence are thought to stimulate aggressive behavior through the same social-cognitive and behavioral mechanisms, such as observational learning, adoption of pro-violent beliefs and attitudes, and priming of aggressive behavior Bradshaw et al. Another, less studied mechanism through which exposure to violence may increase violent behavior is emotional and physiological desensitization to violence, defined as diminished emotional and physiological reactivity following repeated encounters with violence Fanti and Avraamides Although emotional and physiological desensitization is likely adaptive for preserving normal functioning among youth faced with overwhelming levels of violence, over time it may contribute to more violent behavior, greater tolerance of violence, and impaired interpersonal relationships Bushman and Anderson ; Engelhardt et al.
Desensitization has been studied primarily as a consequence of exposure to violent video games e. Despite the many commonalities between real-life and media violence and their effects on adjustment, these two types of exposure to violence rarely have been studied together. Thus, this study examines emotional and physiological desensitization to both real-life and televised violence among late adolescents and emerging adults.
In general, exposure to real-life violence in youth is associated with elevated internalizing symptoms, but the associations are weaker compared to links with externalizing problems and are less consistent across studies Fowler et al. Emotional desensitization has been offered as a possible explanation for these weaker and inconsistent findings e. In fact, several studies investigated and found curvilinear relationships between exposure to community violence and internalizing symptoms that are consistent with the desensitization hypothesis Gaylord-Harden et al.
These studies found the same pattern across three different samples of early adolescents mean ages By contrast, mixed findings have been reported for anxiety symptoms. One study found a quadratic pattern similar to depression Mrug et al. Although gender differences were not investigated in these aforementioned studies, another investigation found the quadratic effect of community violence on a specific type of anxiety PTSD symptoms among adolescent females, but not males McCart et al.
The authors speculated that the lower levels of PTSD symptoms among females exposed to high levels of community violence may not reflect desensitization, but perhaps greater access to certain protective factors by females, such as emotional support from parents. The youth studied by McCart et al. It is possible that emotional desensitization is more likely to occur among younger adolescents who may have fewer coping resources. Surprisingly little research has examined internalizing problems in relationship to television or movie violence. In one study, children and adolescents age who spent more time watching television reported more PTSD symptoms, even after accounting for exposure to real-life violence Singer et al.
Although this cross-sectional finding could reflect a role of TV violence in trauma symptoms, it could also be explained by traumatized youth spending more time watching TV. Although significant, the effect of TV time also was substantially smaller compared to the effects of real-life violence, suggesting that any possible effects of TV violence on internalizing problems are likely very small. However, this study did not evaluate any possible emotional desensitization effects e. Nevertheless, several studies suggest that emotional desensitization to televised violence occurs both in the short-term e.
In one experimental study, male college students reported increased depressive and anxiety symptoms after watching a violent movie, but these negative emotional reactions diminished after several days of repeated exposure to violent movies Linz et al. Similarly, children years who frequently watched television reported feeling less frightened and worried about television violence van der Molen and Bushman , which could reflect long-term emotional desensitization, but also a self-selection of less anxious children into more frequent TV viewing.
Thus, the evidence for emotional desensitization following exposure to televised violence is very limited, and more research on this topic is needed. Despite the common assumption that exposure to real-life violence dulls empathy for others e. Early studies of young children ages exposed to child abuse, neglect, and domestic violence documented the children's lower levels of empathy Hinchey and Gavelek ; Main and George , but a more recent investigation found no association between childhood age exposure to domestic violence and empathy in adolescence mean age 14 McCloskey and Lichter Similarly, exposure to community violence was not related to empathy in several studies of children and adolescents, with mean ages ranging from 10 to 17 Funk et al.
Together, these findings suggest that, among school-aged children and adolescents, exposure to community or family violence bears no relationship to empathy. Another possibility, which has not yet been empirically investigated, is that there may be a curvilinear e. Perhaps exposure to a limited amount of violence increases one's empathy, but repeated exposure to violence decreases empathy as a part of the desensitization process. Stronger evidence links diminished empathy with exposure to movie violence. Viewing sexually violent movies led to less empathy for victims of violence several days later in experimental studies with male college students Linz et al.
Experimental and field studies also documented less helping behavior following exposure to movie violence, which could reflect decreased empathy although empathy was not measured directly in these studies. For instance, year old children randomly assigned to watch a violent video took longer to seek help for a staged fight among other children, compared to peers watching a nonviolent video Drabman and Thomas ; Molitor and Hirsch Similarly, adults who just watched a violent film at the movie theatre took longer to help an injured individual than those who watched a nonviolent film or those arriving to see either type of movie Bushman and Anderson A correlational study that measured self-reported empathy among year old children found that it correlated negatively with exposure to movie violence, but was not uniquely predicted by movie violence once other types of violence were included in the model videogame, TV, and real-life violence; Funk et al.
No studies have tested possible curvilinear relationship between long-term exposure to movie violence and empathy. However, a quadratic relationship has been demonstrated in the short-term: As college students watched nine 2-minute violent scenes, their sympathy for the victims increased and then decreased to below initial levels Fanti et al. This finding was interpreted by the authors as evidence for desensitization to violence. Thus, curvilinear effects of movie violence on empathy warrant further investigation. Additionally, previous studies of both real-life and media violence have focused exclusively on emotional empathy, so possible effects of violence on cognitive empathy remain to be determined.
As a highly emotionally distressing experience, it is possible that violence has stronger effects on emotional than cognitive aspects of functioning. Thus, high levels of exposure to violence, both in real-life and media, may be more likely to produce desensitization in emotional identification with others than in more cognitive perspective taking. As a disturbing and stressful experience, exposure to violence is assumed to stimulate the physiological stress response Kliewer, , which involves two physiological processes: Thus, acute exposure to violence should produce short-term increases in both cortisol and blood pressure.
With chronic stress, the repeated activation of the physiological stress response may lead to long-term increases in baseline levels of cortisol and blood pressure, which in turn contribute to various physiological and psychological problems, such as hypertension, depression, and learning deficits Coughlin ; Lupien et al. Both animal and human studies suggest that the physiological effects of stress are greater and longer-lasting during adolescence than adulthood Lupien et al.
As expected, adolescents exposed to violence in their communities had higher resting blood pressure and cortisol levels Murali and Chen ; Wilson et al. However, other studies found lower resting blood pressure Cooley-Quille and Lorion ; Krenichyn et al. Interestingly, these latter studies sampled youth from more disadvantaged, higher crime urban areas than the former studies, suggesting that very high levels of exposure to violence and related stressors may be associated with chronically low levels of the physiological stress system activation, perhaps due to physiological desensitization.
Thus, a nonlinear relationship between exposure to violence and baseline physiological functioning may exist, but this possibility has not been studied. However, the discrepancies could also be explained by other methodological differences among the studies or the presence of different, unmeasured moderating factors in each sample. Although gender differences have not been investigated in most of these studies, Kliewer found that witnessing community violence was associated with lower blood pressure in boys but not girls. She speculated that boys may be more affected by exposure to violence because they have lower access to internal and external coping resources than girls.
Besides altering baseline physiological functioning, exposure to chronic stress may also affect short-term reactivity to acute stress Coughlin Studies examining physiological responses to acute stress generally have found lower physiological reactivity among youth exposed to real-life violence. For instance, higher exposure to real-life violence was associated with lower blood pressure increase among diverse samples of children and adolescents mean ages 11 and 16; Clark et al.
Similarly, youth mean age 11 exposed to high levels of community violence had lower cortisol elevations after watching a violent video Kliewer However, others have found no differences in heart rate reactivity between youth with high vs. Thus, more research may be needed to examine the links between exposure to violence and physiological reactivity.
Studies of movie violence have focused primarily on physiological reactivity rather than resting levels of physiological variables, perhaps reflecting the assumption that media violence would have only short-term but not long-term effects on physiological functioning. The findings generally show associations between exposure to movie violence and diminished physiological reactivity to violent videos, as reviewed in detail below.
Experimental studies demonstrated that viewing a violent movie led to lower skin conductance among children Thomas et al. Interestingly, these effects have not replicated among female college students in the latter study, perhaps because females may be less likely to experience physiological desensitization. Although less studied, long-term physiological desensitization effects have also been suggested. In several older studies, children who spent more time watching television showed less physiological arousal skin conductance and blood volume in response to violent scenes Cline et al.
These results have been interpreted as indicating physiological desensitization to violent programming, but they could also reflect self-selection of children with lower levels of physiological reactivity to heavier television viewing. In a more recent investigation, college students reporting high exposure to media violence had lower skin conductance in response to watching a violent video clip, but blood pressure or cortisol were not assessed Krahe et al. In sum, the evidence suggests that exposure to violent media leads to short-term reductions in physiological response to televised violence, but longer-term effects on baseline physiological functioning and reactivity are understudied.
Additionally, only linear effects of movie violence on physiological arousal have been tested, and gender differences have been suggested but not systematically evaluated. The evidence suggests that high levels of exposure to real-life and movie violence are associated with diminished emotional distress, emotional empathy, and physiological reactivity, suggesting the presence of emotional and physiological desensitization.
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However, some of these findings are inconsistent across studies, which could be due to methodological differences across studies, presence of different unmeasured moderators, or nonlinear effects of exposure to violence on functioning that have not been typically tested. Possible gender differences in desensitization also have gone largely unaddressed, despite some evidence for their existence. As reviewed above, one study indicated emotional desensitization for PTSD symptoms among females but not males McCart et al. Although it is difficult to draw any conclusions from these few studies, it is important to further evaluate the possibility of gender differences in different types of desensitization.
Additionally, little research has focused on the relationship between exposure to violence and cognitive empathy or on the effect of movie violence on general emotional and physiological functioning. Thus, this study examines linear and quadratic effects of exposure to real-life and movie violence on PTSD symptoms, cognitive and emotional empathy, and physiological functioning, as well as emotional and physiological reactivity to movie violence. We focus on systolic and diastolic blood pressure as measures of physiological functioning, because they represent a major system involved in the physiological response to stress and their elevated levels are linked with substantial morbidity and mortality later in life Coughlin Based on the literature reviewed, we hypothesize that exposure to real-life and movie violence will show quadratic relationships with PTSD symptoms, empathy, baseline blood pressure and emotional and physiological of reactivity, so that PTSD symptoms, empathy, and baseline blood pressure, as well as emotional and physiological reactivity, will peak at moderate levels of exposure but show reductions at high levels.
Gender differences in all effects will be explored, but due to the paucity of research on this topic no directional hypotheses are offered. Participants were college students recruited from introductory psychology classes at a mid-sized public university located in a metropolitan area in the Southeastern U. The study was approved by the university institutional review board.
The sample consisted of students mean age The Community Experiences Questionnaire Schwartz and Proctor assessed lifetime exposure to violence. The measure includes 14 items assessing witnessing violence e. Items were rated from 0 never to 3 lots of times. Exposure to media violence was measured with four items. The two media violence items were rated on a scale from 1 almost never to 4 almost always , or 0 I don't engage in this activity. Consistent with other studies of media violence Funk et al. Participants rated how much each symptom bothered them the last month on a five-point scale from 1 not at all to 5 extremely.
Empathy was measured with three subscales of the Interpersonal Reactivity Index, a multidimensional measure of empathy Davis The Empathic Concern scale includes seven items that assess feelings of concern and sympathy for others in distress, or emotional empathy e. Finally, the seven items on the Fantasy scale assess daydreaming and emotional identification with fictional characters in movies, books and plays e.
The clips came from the following movies and showed the following scenes: Man on Fire — shooting resulting in death and injury to multiple characters, witnessed by a young girl who grieves over one character who was shot; Platoon — soldiers yelling at, shoving, hitting, shooting at and ultimately killing a disabled civilian; Precious — two women pushing, fighting and throwing heavy objects at each other, with an infant present and in danger of being injured or killed; Leon: The Professional — shooting resulting in death and injury of multiple characters, witnessed by a boy; and Saving Private Ryan — soldiers shooting and killing each other, fist fighting, stabbing and strangling that leads to multiple deaths.
The total duration of the clips was 11 minutes 34 seconds, with each clip lasting minutes. In addition, five nonviolent clips were selected from a pool of 11 clips using the same pilot procedures. These clips came from the following movies and showed the following scenes: Twister — family rushing to an underground shelter during a tornado; Crash — man rescuing a woman from a crashed car that starts burning; Speed — rescue team saving people from a fast riding bus with a bomb on board; and Castaway — one scene showing a man trying to save himself when an airplane crashes in the ocean; another scene where a man tries to get away from an island on a handmade boat through rough waves.
Participants were tested individually at a university laboratory.
After providing written informed consent, students were left alone in a private room to answer demographic questions and complete computer questionnaires assessing exposure to real-life and media violence, PTSD symptoms, and empathy. Sensors for cardiovascular monitoring were then attached and participants were instructed to sit quietly for 10 minutes while baseline measures were taken. Immediately after viewing each clip, participants rated how anxious, distressed, and fearful they felt while watching the last movie clip, with the questions presented in random order. At the end of the session, participants watched a neutral video clip to dispel any negative effects of the violent videos and were debriefed and dismissed.
Measurements were taken every 30 sec throughout baseline and video clip presentation. Baseline measures were computed by averaging readings during the last 2 minutes of the minute baseline period. Measures from the first 8 minutes of the resting period are typically not used because blood pressure is still declining to a true resting level Wright et al.
Blood pressure during each of the five video clips was computed as the average of all readings taken during viewing of that clip. Baseline values were subtracted from these averages to yield reactivity scores for each measure. Univariate distributions of all variables were examined; four univariate outliers were truncated to 3. Exposures to real-life and media violence were positively skewed; they were normalized by square root transformations prior to subsequent analyses. Bivariate associations among variables were examined with correlations and t-tests.
The effects of real-life and media violence on PTSD symptoms, empathy and baseline SBP were tested with hierarchical multiple regressions. At Step 2, we added exposure to real-life violence and exposure to media violence both centered at zero and their squares to assess quadratic effects ; linear and quadratic effects were entered together because they were considered equally important. At Step 3, we entered interactions of gender with both main and squared effects of real-life and media violence; these interactions tested whether the linear and quadratic relationships between exposure to violence and outcomes varied by gender.
Emotional and physiological responses to the violent videos were evaluated for the participants randomly assigned to the violent movie condition. There were two outcome variables: Because emotional distress and SBP change were assessed separately for each of the five clips, each participant had five separate observations for each outcome. To model the observations as nested within participants and dependent on time clip number , multilevel modeling using SAS 9.
The multilevel models estimated the intercept level of emotional distress or SBP change from baseline during the middle clip and slope average change in emotional distress or SBP from one clip to the next for each participant. Baseline resting SBP was also included for the analyses of SBP change, because the amount of change partly depends on baseline level.
At Step 2, exposure to real-life violence and exposure to media violence and their squares to assess quadratic effects were entered as predictors of the intercept and slope. These terms are entered in the model as main effects predicting intercept and interactions with clip predicting slopes. In parallel with the multiple regressions, linear and quadratic effects were included in the same step because they were of equal theoretical importance.
At Step 3, gender differences in the effects of exposure to violence on the outcomes were tested by adding interactions of gender with clip and each term from Step 2. All predictor variables were centered at zero to facilitate the interpretation of coefficients. To evaluate whether reactivity effects related to exposure to violence were specific to violent video content, the same multilevel analyses were conducted for the participants randomized to watch the nonviolent clips. Descriptive statistics and correlations of all variables are presented in Table 1.
On average, participants reported the equivalent of experiencing 16 different acts of violence once or 8 different types several times; and 10 hours a week of TV and movies with some violent content. Average levels of empathic concern, perspective taking and fantasy were above the midpoint of the scale, indicating that participants felt that the items described them well. Exposure to media violence was associated with greater perspective taking.
PTSD symptoms were related to higher fantasy. Empathic concern, perspective taking, and fantasy were weakly positively related. The results of multiple regressions evaluating linear and quadratic effects of exposure to real-life and media violence on PTSD symptoms, empathy and baseline SBP are listed in Table 2. At Step 1, female gender was associated with greater empathic concern and fantasy. After adjusting for demographic variables, exposure to real-life violence showed positive linear associations with PTSD symptoms and fantasy and negative quadratic associations with empathic concern and perspective taking Step 2.
As shown in Figure 1 , both empathy variables reached highest estimated levels among participants with medium levels of real-life violence exposure compared to those with lower or higher levels of exposure. Exposure to media violence only showed a positive linear relationship with perspective taking, but was unrelated to PTSD symptoms, emotional empathy, and fantasy.
At Step 3, no interactions with gender reached significance, indicating that the associations between exposure to real-life or media violence and outcomes did not differ between males and females. Model-based estimates showing the curvilinear relationship between exposure to real-life violence and empathy. Results of the multilevel models estimating the effects of exposure to violence on emotional and physiological reactivity to violent movies are presented in Table 3.
At Step 1, the positive and significant intercepts indicate that during the middle clip, participants experienced moderate emotional distress 1. The significant positive effects of clip for emotional distress indicates that participants experienced increasing levels of emotional distress as they watched the series of five violent movie clips, but the effect of clip was not significant for SBP, indicating no significant changes from one clip to the next just an overall increase from baseline, as shown by the intercept.
At Step 2, exposure to real-life and media violence showed no linear or quadratic associations with the intercept or slope of emotional distress. For SBP, there was a positive quadratic effect of media violence on the intercept, suggesting greater overall increase in SBP for those exposed to high levels of media violence, as well as negative linear and quadratic effects of media violence on the slope, suggesting faster decrease in SBP for those exposed to high levels of movie violence throughout the viewing period. Estimated trajectories of SBP change for individuals with low, average and high levels of exposure to movie violence show the combination of these effects in Figure 2.
Those with low levels of exposure experienced somewhat higher initial elevation in blood pressure followed by slight increase over time. Model-based estimates demonstrating changes in blood pressure while watching of violent movie clips as a function of previous exposure to media violence. Low and high levels of exposure to media violence correspond to 1 SD below and above the mean, respectively. At Step 3, there were no gender differences in the effects of violence exposure on SBP.
However, gender moderated the effect of real-life violence on the slope of emotional distress during the viewing period. Figure 3 shows the estimated trajectories of distress for males and females with low vs. It shows that emotional distress increased with each clip for females regardless of their exposure to real-life violence, as well as for males with low levels of exposure. By contrast, emotional distress decreased with each clip for males exposed to high levels of real-life violence. Model-based estimates illustrating gender differences in the effect of exposure to real-life violence on emotional distress during watching violent movie clips.
Ratings of distress could range from 0 not at all to 4 extremely. Low and high levels of exposure to violence correspond to 1 SD below and above the mean, respectively. When the multilevel models were repeated for the participants randomized to view nonviolent videos, the only significant effects emerged in Step 1. Theoretical accounts and limited empirical evidence suggest that repeated exposure to violence, both in real-life and through media, produces emotional and physiological desensitization characterized by diminished emotional distress and empathy, as well as reduced emotional and physiological reactivity to further violence Krahe and Moller ; Krahe et al.
Over time, repeated exposure to violence is also thought to alter baseline physiological functioning, including blood pressure Kliewer The negative effects of exposure to violence are particularly salient during adolescence Fischer et al. This study was the first to systematically evaluate multiple aspects of desensitization in relationship to both real-life and media violence experienced by late adolescents, as well as gender differences in these relationships.
Because desensitization may follow a more complex curvilinear pattern Ng-Mak et al. The results revealed that exposure to real-life violence had a positive linear relationship with PTSD symptoms and fantasy, but a quadratic relationship with emotional and cognitive empathy, so that empathy was the highest at medium levels of exposure but decreased at high levels of real-life violence.
Neither type of exposure to violence was related to baseline blood pressure, and there were no gender differences in these relationships. Viewing 11 minutes of high-action violent or nonviolent videos was associated with increased blood pressure over resting baseline, and moderate levels of emotional distress that generally increased with each successive clip. Although these general reactions did not differ between violent vs. Specifically, males exposed to high levels of real-life violence exhibited decreasing emotional distress with each clip, compared to increasing distress reported by males with lower levels of exposure and females.
Additionally, those with average or low exposure to movie violence had stable or increasing blood pressure while viewing the violent videos, whereas those with higher exposure to movie violence experienced rapid increase in blood pressure followed by decrease. Taken together, these results support the hypothesis that high levels of exposure to real-life violence are related to diminished empathy and, for males only, decreasing emotional distress in response to viewing violence. A novel contribution to the literature on youth exposed to real-life violence is the demonstration of curvilinear relationships between exposure to violence and empathy.
Although the magnitude of this effect was small to medium sized, it replicated across both cognitive and emotional facets of empathy. Prior studies have only evaluated linear relationships between exposure to violence and empathy, and did not find any evidence of such linear relationships among older children and adolescents Funk et al. Our results replicated the absence of a linear relationship, but revealed a quadratic pattern of higher empathy among youth exposed to medium levels of real-life violence compared to those with lower or higher levels.
These results imply that future studies on exposure to violence and empathy should evaluate possible curvilinear relationships to replicate these findings and determine when in development such relationships appear. The obtained quadratic pattern for empathy suggests that individuals exposed to some real-life violence may have better ability to understand others and share their emotions than those not exposed to any violence, but that this ability to understand and empathize with others may deteriorate at high levels of exposure to violence.
It is possible that some exposure to violence may sharpen perspective taking and empathy, because people can relate to traumatic experiences, pain and distress of others. Because limited levels of exposure to violence may be psychologically manageable, successful coping with this experience may promote empathy for others. This hypothesis should be further explored in the literature, particularly with respect to specific characteristics of exposure to violence that may be more or less likely to foster empathy. For instance, proximity to the violence e.
By contrast, at high levels of exposure to real-life violence individuals report lower levels of empathy, perhaps because of interference from more severe trauma symptoms Nietlisbach et al. Diminished empathy at high levels of exposure to violence may also serve as a protective mechanism to shield individuals from assuming more emotional and cognitive burdens than they can handle.
These interpretations need to take into account the levels of violence and trauma experienced by the participants. Although we sampled a nonclinical population of college students, many of them reported relatively high levels of both exposure to violence and trauma symptoms. These rates of exposure to violence and trauma symptoms are very similar to other studies with college students conducted across the U.
Interestingly, there was no indication of desensitization for anxiety, as measured with PTSD symptoms. Instead, higher levels of exposure to real-life violence were associated with more PTSD symptoms. This medium-to-large-sized relationship was the strongest effect obtained in the regression analyses. These results are consistent with other studies finding mostly linear relationships between exposure to real-life violence and anxiety among adolescents Gaylord-Harden et al.
It is likely that the traumatic nature of real-life violence contributes to increased intrusive thoughts, avoidance, dysphoria and anxious arousal characteristic of PTSD at high levels of exposure to violence. However, higher PTSD symptoms could also partly reflect emotional desensitization, as some PTSD items evaluate emotional detachment and restricted affect. Detachment from one's own emotions and avoidance experienced by individuals exposed to higher levels of real-life violence may contribute to their increased tendency to daydream and identify with fictional characters, as indicated by elevated fantasy scores in this study small to medium effect.
Similar to our findings, Singer and colleagues reported moderate associations between exposure to violence and dissociation in children and young adolescents, with their dissociation scale tapping fantasy as well as overt dissociation Briere Some of the fantasies employed by individuals exposed to high levels of violence may involve violent content, as suggested by studies linking exposure to violence with engagement in aggressive fantasies among children and adolescents Guerra et al.
This escape to the fantasy world may not be entirely adaptive for young people exposed to violence, as higher fantasy scores are related to interpersonal difficulties and loneliness Davis Thus, fantasy may serve as an avoidant coping strategy that does not promote successful coping with experiences of real-life violence. Future research on exposure to violence should distinguish between aggressive and nonaggressive fantasies and examine their long-term consequences on adjustment.
Contrary to expectations, exposure to real-life violence was unrelated to resting levels of blood pressure. Other studies also found generally weak and nonsignificant relationships between lifetime total exposure to violence and SBP among adolescents, although the results were somewhat stronger for the dimension of frequency of exposure to violence Murali and Chen Meta-analyses of studies with adults showed small to medium-sized association between PTSD diagnosis vs.
Alternatively, the effects of exposure to violence on baseline blood pressure may only be apparent when comparing more extreme groups e. The effect of exposure to real-life violence on reactivity to violent videos varied by gender and only involved emotional reactions, not changes in blood pressure. Specifically, males who had been exposed to higher levels of real-life violence reported decreasing emotional distress through the viewing period, compared to increasing distress among males exposed to lower levels of real-life violence and females regardless of their exposure history a medium sized effect.
These results are consistent with the hypothesized desensitization pattern of less emotional reactivity to violence among those with higher levels of exposure to real-life violence. One explanation for the gender difference may be a greater tendency of males to develop desensitization, perhaps because they are generally exposed to more violence than females Finkelhor et al. This hypothesis is supported by reports of physiological desensitization among males but not females Kliewer ; Linz et al.
Another explanation may be related to the violent scenes shown in this study depicting primarily males as victims and perpetrators of violence reflecting general gender patterns in violent movies; Smith et al. Perhaps males were more likely to identify with the same-sex victims than females Calvert et al. Finally, it is possible that males exposed to higher levels of real-life violence were more aware of the fictitious nature of the movie violence and therefore experienced declining distress.
Clearly, more research is needed to replicate and elucidate these findings.
Exposure to movie violence was modestly positively correlated with exposure to real-life violence, consistent with other studies of older children and adolescents Boxer et al. To better understand this relationship, we have examined correlations between perspective taking and the four variables that were combined to measure exposure to televised violence. However, exposure to movie violence was not related to PTSD symptoms, fantasy, diminished empathy or baseline blood pressure, providing no evidence of longer-term trauma or desensitization.
Our findings may not generalize to younger youth who may be more vulnerable and less able to distinguish between reality and fiction Wright et al. Participants reported gradually increasing emotional distress as they watched the violent movie clips, confirming the distressing nature of the movie scenes selected for use in this study.
Interestingly, the same effect was observed for the nonviolent clips that showed people's lives endangered by natural phenomena tornado, waves , or vehicle crashes car and airplane crash, impending bus crash but no interpersonal violence. Similarly, moderate elevations in blood pressure were experienced by participants viewing both types of videos, which are consistent with response to stressful stimuli in a passive viewing context Sherwood et al.
Since emotional distress increased throughout the viewing period, there was no evidence of immediate desensitization. Others who found emotional desensitization to violent movies included much longer exposure, presenting full movies over 5 days Linz et al. Specifically, high levels of previous exposure to televised violence were associated with initially high 4.
In contrast, those with low previous exposure to movie violence exhibited moderate initial blood pressure increase about 2. The pattern for individuals with medium levels of exposure was consistent with our hypothesis of desensitization, involving less physiological reactivity compared to those with low levels of exposure. However, the pattern for the highly exposed group was unexpected.