Ventromedial prefrontal cortex activation and neurofeedback modulation during episodic future thinking for individuals with suicidal thoughts and behaviors.

Individuals experiencing suicidal thoughts and behaviors (STBs) show less specificity and positivity during episodic future thinking (EFT). Here, we present findings from two studies aiming to (1) further our understanding of how STBs may relate to neural responsivity during EFT and (2) examine the feasibility of modulating EFT-related activation using real-time fMRI neurofeedback (rtfMRI-nf). Study 1 involved 30 individuals with major depressive disorder (MDD; half with STBs) who performed an EFT task during fMRI, for which they imagined personally-relevant future positive, negative, or neutral events. Positive EFT elicited greater ventromedial prefrontal cortex (vmPFC) activation compared to negative EFT. Importantly, the MDD + STB group exhibited reduced vmPFC activation across all EFT conditions compared to MDD-STB; although EFT fluency and subjective experience remained consistent across groups. Study 2 included rtfMRI-nf focused on vmPFC modulation during positive EFT for six participants with MDD + STBs. Results support the feasibility and acceptability of the rtfMRI-nf protocol and quantitative and qualitative observations are provided to help inform future, larger studies aiming to examine similar neurofeedback protocols. Results implicate vmPFC blunting as a promising treatment target for MDD + STBs and suggest rtfMRI-nf as one potential technique to explore for enhancing vmPFC engagement.

Electrophysiological investigation of reward anticipation and outcome evaluation during slot machine play.

Slot machines are a popular form of gambling, offering a tractable way to experimentally model reward processes. This study used a 3-reel slot paradigm to assess psychologically distinct phases of reward processing, reflecting anticipation, and early- and late-stage outcome processing. EEG measures of winning, nearly missing (a losing outcome revealed at the final, third reel), and "totally" missing (a losing outcome revealed earlier, at the second reel) were collected from healthy adults (n=54). Condition effects were evaluated in: i) event-related potential (ERP) components reflecting anticipatory attention (stimulus preceding negativity, SPN) and outcome processing (reward positivity, RewP and late-positive potential, LPP) and ii) total power and phase synchrony of theta and delta band oscillations. Behaviorally, trial initiation was fastest after a near miss outcome and slowest after a winning outcome. As expected, a significant SPN was observed for possible wins (AA) vs. total misses (AB), consistent with reward anticipation. Larger win (AAA) vs. near miss (AAB) amplitudes were observed for the RewP; LPP amplitudes were largest for wins (AAA), intermediate for near misses (AAB), and smallest for total misses (ABC), reflecting significant early (RewP) and late-stage (LPP) outcome processing effects. There was an effect of reel position on the RewP, with larger amplitude in the final reel (AAA-AAB) relative to the 2nd-reel locked difference waves (AA-AB). Across all outcomes, near misses elicited the largest and most phase-synchronized theta responses, while wins elicited larger and more phase-synchronized delta responses than total misses, with delta band measures not distinguishing between near misses and wins. . Phase locking measures contrasting win vs. near miss delta and theta synchronization, within time windows corresponding to ERP measurements, covaried with RewP, but not SPN or LPP, amplitude. Lastly, EEG measures showed differential relationships with age and self-reported consummatory pleasure. In the context of slot machine play, where reward anticipation and attainment place minimal demands on effort and skill, ERP and time-frequency methods capture distinct neurophysiological signatures of reward anticipation and outcome processing.

Change in neural response during emotion regulation is associated with symptom reduction in cognitive behavioral therapy for anxiety disorders.

BACKGROUND: Anxiety disorders are debilitating conditions that can be treated with cognitive behavioral therapy (CBT). Increased understanding of the neurobiological correlates of CBT may inform treatment improvements and personalization. Prior neuroimaging studies point to treatment-related changes in anterior cingulate, insula, and other prefrontal regions during emotional processing, yet to date the impact of CBT on neural substrates of "top down" emotion regulation remains understudied. We examined the relationship between symptom changes assessed over the course of CBT treatment sessions and pre- to post-treatment neural change during an emotion regulation task. METHOD: In the current study, a sample of 30 participants with panic disorder or generalized anxiety disorder completed a reappraisal-based emotion regulation task while undergoing fMRI before and after completing CBT. RESULTS: Reduced activation in the parahippocampal gyrus was observed from pre- to post-treatment during periods of reducing versus maintaining emotion. Parahippocampal activation was associated with change in symptoms over the course of treatment and post-treatment responder status. Results suggest that, from pre- to post-CBT, participants demonstrated downregulation of neural responses during effortful cognitive emotion regulation. LIMITATIONS: Effects were not observed in frontoparietal systems as would be hypothesized based on prior literature, suggesting that treatment-related change could occur outside of fronto-parietal and limbic regions that are central to most models of neural functioning in anxiety disorders. CONCLUSIONS: Continued work is needed to better understand how CBT affects cognitive control and memory processes that are hypothesized to support reappraisal as a strategy for emotion regulation.

Altered interoceptive activation before, during, and after aversive breathing load in women remitted from anorexia nervosa.

BACKGROUND: The neural mechanisms of anorexia nervosa (AN), a severe and chronic psychiatric illness, are still poorly understood. Altered body state processing, or interoception, has been documented in AN, and disturbances in aversive interoception may contribute to distorted body perception, extreme dietary restriction, and anxiety. As prior data implicate a potential mismatch between interoceptive expectation and experience in AN, we examined whether AN is associated with altered brain activation before, during, and after an unpleasant interoceptive state change. METHODS: Adult women remitted from AN (RAN; n = 17) and healthy control women (CW; n = 25) underwent functional magnetic resonance imaging during an inspiratory breathing load paradigm. RESULTS: During stimulus anticipation, the RAN group, relative to CW, showed reduced activation in right mid-insula. In contrast, during the aversive breathing load, the RAN group showed increased activation compared with CW in striatum and cingulate and prefrontal cortices (PFC). The RAN group also showed increased activation in PFC, bilateral insula, striatum, and amygdala after stimulus offset. Time course analyses indicated that RAN responses in interoceptive processing regions during breathing load increased more steeply than those of CW. Exploratory analyses revealed that hyperactivation after breathing load was associated with markers of past AN severity. CONCLUSIONS: Anticipatory deactivation with a subsequent exaggerated brain response during and after an aversive body state may contribute to difficulty predicting and adapting to internal state fluctuation. Because eating changes our interoceptive state, restriction may be one method of avoiding aversive, unpredictable internal change in AN.

Early life stress and the anxious brain: evidence for a neural mechanism linking childhood emotional maltreatment to anxiety in adulthood.

BACKGROUND: Childhood emotional maltreatment (CEM) increases the likelihood of developing an anxiety disorder in adulthood, but the neural processes underlying conferment of this risk have not been established. Here, we test the potential for neuroimaging the adult brain to inform understanding of the mechanism linking CEM to adult anxiety symptoms. METHOD: One hundred eighty-two adults (148 females, 34 males) with a normal-to-clinical range of anxiety symptoms underwent structural and functional magnetic resonance imaging while completing an emotion-processing paradigm with facial expressions of fear, anger, and happiness. Participants completed self-report measures of CEM and current anxiety symptoms. Voxelwise mediation analyses on gray-matter volumes and activation to each emotion condition were used to identify candidate brain mechanisms relating CEM to anxiety in adulthood. RESULTS: During processing of fear and anger faces, greater amygdala and less right dorsolateral prefrontal (dlPFC) activation partially mediated the positive relationship between CEM and anxiety symptoms. Greater right posterior insula activation to fear also partially mediated this relationship, as did greater ventral anterior cingulate (ACC) and less dorsal ACC activation to anger. Responses to happy faces in these regions did not mediate the CEM-anxiety relationship. Smaller right dlPFC gray-matter volumes also partially mediated the CEM-anxiety relationship. CONCLUSIONS: Activation patterns of the adult brain demonstrate the potential to inform mechanistic accounts of the CEM conferment of anxiety symptoms. Results support the hypothesis that exaggerated limbic activation to negative valence facial emotions links CEM to anxiety symptoms, which may be consequent to a breakdown of cortical regulatory processes.

Increased anterior insula activity in anxious individuals is linked to diminished perceived control.

Individuals with high-trait anxiety frequently report decreased perceived control. However, it is unclear how these processes are instantiated at a neural level. Prior research suggests that individuals prone to anxiety may have exaggerated activity in the anterior insula and altered activity in the cingulate cortex during anticipation of aversive events. Thus, we hypothesized that anxiety proneness influences anterior insula activation during anticipation of unpredictable threat through decreased perceived control. Forty physically healthy adults underwent neuroimaging while they explored computer-simulated contexts associated either with or without the threat of an unpredictable shock. Skin conductance, anxiety ratings and blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging were used to assess responses to threat versus no threat. Perceived control was measured using the Anxiety Control Questionnaire-Revised. Mediation analysis examined how anxiety proneness influenced BOLD activity. Anticipation of unpredictable threat resulted in increased skin conductance responses, anxiety ratings and enhanced activation in bilateral insula, anterior midcingulate cortex (aMCC) and bed nucleus of the stria terminalis. Individuals with greater anxiety proneness and less perceived control showed greater activity in dorsal anterior insula (dAI). Perceived control mediated the relationship between anxiety proneness and dAI activity. Increased dAI activity was associated with increased activity in aMCC, which correlated with increased exploratory behavior. Results provide evidence that exaggerated insula activation during the threat of unpredictable shock is directly related to low perceived control in anxiety-prone individuals. Perceived control thus may constitute an important treatment target to modulate insula activity during anxious anticipation in anxiety-disordered individuals.

Intolerance of uncertainty as a mediator of reductions in worry in a cognitive behavioral treatment program for generalized anxiety disorder.

Growing evidence suggests that intolerance of uncertainty (IU) is a cognitive vulnerability that is a central feature across diverse anxiety disorders, including generalized anxiety disorder (GAD). Although cognitive behavioral therapy (CBT) has been shown to reduce IU, it remains to be established whether or not reductions in IU mediate reductions in worry. This study examined the process of change in IU and worry in a sample of 28 individuals with GAD who completed CBT. Changes in IU and worry, assessed bi-weekly during treatment, were analyzed using multilevel mediation models. Results revealed that change in IU mediated change in worry (ab = -0.20; 95% CI [-.35, -.09]), but change in worry did not mediate change in IU (ab = -0.16; 95% CI [-.06, .12]). Findings indicated that reductions in IU accounted for 59% of the reductions in worry observed over the course of treatment, suggesting that changes in IU are not simply concomitants of changes in worry. Findings support the idea that IU is a critical construct underlying GAD.

Increased brain response to appetitive tastes in the insula and amygdala in obese compared with healthy weight children when sated.

OBJECTIVE: There is evidence of altered neural taste response in female adolescents who are obese (OB), and in adolescents who are at risk for obesity. To further understand risk factors for the development of overeating and obesity, we investigated response to tastes of sucrose and water in 23 OB and healthy weight (HW) children. METHODS AND DESIGN: Thirteen HW and 10 OB 8-12-year-old children underwent functional magnetic resonance imaging while tasting sucrose and water. Additionally, children completed an eating in the absence of hunger paradigm and a sucrose-liking task. RESULTS: A region of interest analysis revealed an elevated BOLD response to taste (sucrose and water) within the bilateral insula and amygdala in OB children relative to HW children. Whole-brain analyses revealed a group by condition interaction within the paracingulate, medial frontal, middle frontal gyri and right amygdala: post hoc analyses suggested an increased response to sucrose for OB relative to HW children, whereas HW children responded more strongly to water relative to sucrose. In addition, OB children, relative to HW, tended to recruit the right putamen as well as medial and lateral frontal and temporal regions bilaterally. CONCLUSION: This study showed increased reactivity in the amygdala and insula in the OB compared with HW children, but no functional differentiation in the striatum, despite differences in the striatum previously seen in older samples. These findings support the concept of the association between increased neural processing of food reward in the development of obesity, and raise the possibility that emotional and interoceptive sensitivity could be an early vulnerability in obesity.

High Thrill and adventure seeking is associated with reduced interoceptive sensitivity: evidence for an altered sex-specific homeostatic processing in high sensation seekers.

OBJECTIVE: The personality trait of sensation seeking (SS) has been traditionally linked to the construct of exteroception, i.e. sensing of the outside world. Little is known about the relationship between SS and interoception, i.e. sensing originating in the body. Interoceptive sensations have strong affective and motivational components that may influence behaviors such as risk-taking in SS. This investigation examined whether interoceptive differences contribute to different behavioral characteristics in SS. METHOD: Using an inspiratory resistive load breathing task, the response to an aversive interoceptive stimulus as a basic homeostatic process was studied in 112 subjects (n=74 females, 38 males). A linear-mixed model approach was used to examine the influence of thrill and adventure seeking (TAS) on the interoceptive response across three levels of breathing resistances (10, 20, 40 cmH2O/L/sec). RESULTS: High relative to low TAS individuals were less responsive in evaluating intensities of perceived choking with increasing inspiratory resistive loads. This effect was driven by male, but not female high TAS individuals and was particularly associated with reduced interoceptive sensitivity in males. CONCLUSION: The conceptualization of SS as primarily driven by exteroceptive stimuli can be expanded to a view of an altered homeostasis in SS, specifically in males.

Prefrontal dysfunction during emotion regulation in generalized anxiety and panic disorders.

BACKGROUND: The mechanisms that contribute to emotion dysregulation in anxiety disorders are not well understood. Two common disorders, generalized anxiety disorder (GAD) and panic disorder (PD), were examined to test the hypothesis that both disorders are characterized by hypo-activation in prefrontal cortex (PFC) during emotion regulation. A competing hypothesis that GAD in particular is characterized by PFC hyper-activation during emotion regulation (reflecting overactive top-down control) was also evaluated. Method Twenty-two medication-free healthy control (HC), 23 GAD, and 18 PD participants underwent functional magnetic resonance imaging (fMRI) during a task that required them to reappraise (i.e. reduce) or maintain emotional responses to negative images. RESULTS: GAD participants reported the least reappraisal use in daily life, and reappraisal use was inversely associated with anxiety severity and functional impairment in these participants. During fMRI, HCs demonstrated greater activation during both reappraisal and maintenance than either GAD or PD participants (who did not differ) in brain areas important for emotion regulation (e.g. dorsolateral and dorsomedial PFC). Furthermore, across all anxious participants, activation during reappraisal in dorsolateral and dorsomedial PFC was inversely associated with anxiety severity and functional impairment. CONCLUSIONS: Emotion dysregulation in GAD and PD may be the consequence of PFC hypo-activation during emotion regulation, consistent with insufficient top-down control. The relationship between PFC hypo-activation and functional impairment suggests that the failure to engage PFC during emotion regulation may be part of the critical transition from dispositionally high anxiety to an anxiety disorder.

The role of the left inferior frontal gyrus in social perception: an rTMS study.

Perceiving and interpreting social information richness is something that humans do automatically whenever they engage in social interactions. Numerous studies have identified neural substrates, including mirror neurons that may enable such social perception. In this study, we temporarily disrupted activity in the left inferior frontal gyrus (LIFG) using repetitive transcranial magnetic stimulation (rTMS). We investigated whether this cortical region, that is hypothesized to include mirror neurons, plays a central role in social perception. The LIFG was stimulated in the experimental condition (n=18), the vertex was targeted in the control condition (n=19). Disrupting LIFG, but not vertex, increased reaction times during an emotion recognition task, and eliminated the suppression of the 8-12Hz EEG µ rhythm, postulated as an index of mirroring activity. The results of this study provide further evidence for the role of the human mirror neuron system (MNS) in social perception, and indicate that the MNS can be measured with EEG.

Happy but not so approachable: the social judgments of individuals with generalized social phobia.

BACKGROUND: We examined social approachability judgments in a psychiatric population that frequently experiences interpersonal difficulties and reduced social satisfaction, individuals with generalized social phobia (gSP). METHODS: Our objective was to broaden the understanding of the social cognitive tendencies of individuals with gSP by systematically investigating their interpretation of positive facial expressions. We hypothesized that approachability ratings would be lower for positive as well as negative emotional faces in the gSP group compared to the healthy comparison group. Each participant evaluated 24 emotional faces presented on a computer screen. Participants first labeled the faces as either happy, disgust, or angry in emotional expression, and then they rated each face's approachability. Analysis of variance and post hoc analyses were used to identify group, emotion, and group by emotion rating differences. RESULTS: Happy face approachability ratings were higher than disgust and anger in both groups. The central finding was that individuals with gSP rated happy faces as less approachable than the healthy participants and that degree of social anxiety was associated with lower approachability ratings within the gSP sample. Explicit approachability judgments of negative faces did not differ as predicted. CONCLUSIONS: Consistent with earlier indirect evidence of interpretation biases of positive social emotional information, this study reveals that individuals with gSP demonstrate explicit, subjective social interpretation biases of overtly positive social feedback. The therapeutic relevance of these results is discussed.

Candidate genes, pathways and mechanisms for bipolar (manic-depressive) and related disorders: an expanded convergent functional genomics approach.

Identifying genes for bipolar mood disorders through classic genetics has proven difficult. Here, we present a comprehensive convergent approach that translationally integrates brain gene expression data from a relevant pharmacogenomic mouse model (involving treatments with a stimulant--methamphetamine, and a mood stabilizer--valproate), with human data (linkage loci from human genetic studies, changes in postmortem brains from patients), as a bayesian strategy of crossvalidating findings. Topping the list of candidate genes, we have DARPP-32 (dopamine- and cAMP-regulated phosphoprotein of 32 kDa) located at 17q12, PENK (preproenkephalin) located at 8q12.1, and TAC1 (tachykinin 1, substance P) located at 7q21.3. These data suggest that more primitive molecular mechanisms involved in pleasure and pain may have been recruited by evolution to play a role in higher mental functions such as mood. The analysis also revealed other high-probability candidates genes (neurogenesis, neurotrophic, neurotransmitter, signal transduction, circadian, synaptic, and myelin related), pathways and mechanisms of likely importance in pathophysiology.

Strain-specific effects of amphetamine on prepulse inhibition and patterns of locomotor behavior in mice.

Several reports describe substantive behavioral differences between strains of mice both at baseline and in response to pharmacological manipulations. For example, mouse strain differences have been reported in prepulse inhibition (PPI) and patterns of locomotor activity, two behavioral processes that are altered by dopamine (DA) agonists such as amphetamine. Here, we characterized acoustic and tactile startle reactivity, acoustic PPI, and both the amounts and spatial patterns of locomotor activity in C57BL/6J, 129SvEv (129S6), and 129SvJ (129X1) mice at baseline and in amphetamine dose-response studies. Because hearing loss is common in numerous strains of mice, we also assessed cross-modal PPI using a light prepulse with an airpuff startle stimulus. The results establish that these three inbred strains of mice display both intra- and cross-modal PPI, and that amphetamine decreases PPI and startle reactivity in a dose-, sensory modality-, and strain-specific manner. Furthermore, the amount of locomotor activity and the spatial pattern of motor sequences are altered differentially after treatment with amphetamine in C57BL/6J and 129X1 mice, but not in 129S6 mice. Given that amphetamine releases presynaptic DA, these findings are consistent with the role of DA in the modulation of PPI and motor patterns in mice. These findings highlight the importance of selecting appropriate strains of mice for behavioral, pharmacological, and genetic studies.

Trait contributions of complex dysregulated behavioral organization in schizophrenic patients.

BACKGROUND: The "temporal architecture" of behavior is a construct that can be used to quantify the structure of behavioral sequences in the temporal domain-for example, by using a two-choice prediction task to investigate how past responses, stimuli, and outcomes influence the decision-making process. Using this task, previous investigations of the temporal architecture of the behavior in schizophrenic patients have identified an increased frequency of alternating highly predictable and highly unpredictable response sequences in the same test session in the same patient. Here, the hypothesis is tested that this dysregulation is stable over time and independent of psychosocial factors and symptomatic fluctuations. METHODS: Ninety-one schizophrenic patients were tested on a 128 trial version of the two-choice prediction task; of those, 58 subjects completed a retest session 40 days later. Three sets of measures were obtained: simple response biases, dynamical entropy, and mutual information functions. These measures were subjected to a factor analysis, and the reliability of the resulting factors was examined. RESULTS: First, three factors were obtained, which quantify 1) the level of dysregulation on this task; 2) the extent to which a win-stay/lose-shift strategy was used; and 3) the amount of simple response perseveration. Second, Crohnbach alpha for these factors was .699, .721, and .458, respectively. Third, there were no significant differences in the level of these factors within individual patients at the two time points. Fourth, neither symptom measures (Scale for the Assessment of Positive Symptoms and Scale for the Assessment of Negative Symptoms subscale scores) nor psychosocial or clinical variables (age, gender, illness duration, medication status) were able to predict the level of these factors at test or at retest. CONCLUSIONS: These results support the hypothesis that the fundamental dysregulation of the temporal architecture of behavior in schizophrenic patients is stable across time and independent of symptomatic status. Future studies will examine the heritability of this dysfunction.

Prefrontal, parietal, and temporal cortex networks underlie decision-making in the presence of uncertainty.

Decision-making in the presence of uncertainty, i.e., selecting a sequence of responses in an uncertain environment according to a self-generated plan of action, is a complex activity that involves both cognitive and noncognitive processes. Using functional magnetic resonance imaging, the neural substrates of decision-making in the presence of uncertainty are examined. Normal control subjects show a significant activation of a frontoparietal and limbic neural system during a two-choice prediction task relative to a two-choice response task. The most prevalent response strategy during the two-choice prediction task was "win-stay/lose-shift," where subjects will repeat the previous response if it successfully predicted the stimulus and switch to the alternative response otherwise. Increased frequency of responses that are consistent with this strategy is associated with activation in the superior temporal gyrus. In comparison, increased frequency of response inconsistent with win-stay/lose-shift is associated with parietal cortex activation. These results support the hypothesis that subjects use a frontoparietal neural system to establish a contingency based decision-making strategy even in the presence of random reinforcement.

Prepulse inhibition deficits and perseverative motor patterns in dopamine transporter knock-out mice: differential effects of D1 and D2 receptor antagonists.

Dopamine is known to regulate several behavioral phenomena, including sensorimotor gating and aspects of motor activity. The roles of dopamine D1 and D2 receptors in these behaviors have been documented in the rat literature, but few reports exist on their role in mice. We used dopamine transporter (DAT) (-/-) mice to examine the behavioral consequences of a chronically hyperdopaminergic state, challenging them with the preferential dopamine D2 receptor antagonist raclopride and D1 receptor antagonist SCH23390. At baseline, DAT (-/-) mice exhibited deficient sensorimotor gating as measured by prepulse inhibition (PPI) of the startle response, exhibited nonfocal preservative patterns of locomotion, and were hyperactive in a novel environment. Pretreatment with raclopride significantly increased PPI in the DAT (-/-) mice, whereas SCH23390 had no significant effect. Blockade of D2 receptors did not affect the predominantly straight patterns of motor behavior produced by the DAT (-/-) mice, but antagonism of D1 receptors significantly attenuated the preservative patterns, producing more of a meandering behavior seen in the DAT (+/+) control mice. Both D1 and D2 receptor antagonists decreased the hyperactivity seen in the DAT (-/-) mice. These findings support the role of the D2, but not the D1, receptor in the modulation of PPI in mice. Furthermore, D1 receptor activation appears to be the critical substrate for the expression of preservative patterns of motor behavior, whereas both D1 and D2 receptors appear to regulate the amount of motor activity.

Recurrent erosions of the cornea: epidemiology and treatment.

PURPOSE: To evaluate the epidemiologic characteristics of a large clinical population of patients with recurrent erosions of the cornea. The efficacy of different modalities of treatment was also evaluated. METHODS: A retrospective chart review of all patients with the diagnosis of recurrent corneal erosion treated between January 1990 and December 1998 was performed. RESULTS: Clinically confirmed recurrent erosions were identified in 104 patients. There were 36 males and 68 females. A history of trauma was present in 47 patients (45%), 30 patients (29%) had epithelial basement membrane dystrophy (EBMD), and 18 patients (17%) had both a history of trauma and evidence of EBMD. More than 87% of all erosions occurred on the inferior third of the cornea. Conservative therapy was used as the primary treatment in 52 patients with a recurrence rate of 6%. Corneal stromal micropuncture was performed on 38 patients with a recurrence rate of 40%. Eleven patients had epithelial debridement with a recurrence rate of 18%. Four patients had a superficial keratectomy with a diamond bur with a recurrence rate of 25%. Only one patient had an excimer phototherapeutic keratectomy, and she had a minor recurrence posttreatment. CONCLUSIONS: In our series, the distribution of trauma and EBMD in patients with recurrent erosions of the cornea is roughly equivalent. Conservative therapy was effective in approximately one half of the patients. All surgical treatment modalities were associated with recurrences. Those patients with both EBMD and trauma were more likely to have a recurrence after treatment. More effective treatment modalities for recurrent erosions of the cornea need to be investigated.

Environmental enrichment and isolation rearing in the rat: effects on locomotor behavior and startle response plasticity.

BACKGROUND: Laboratory rats exhibit behavioral changes that reflect a continuum of early life experience, from isolation-reared to socially reared to enrichment-reared conditions. In this study, we further characterize the behavioral effects of isolation, social, and enriched rearing on locomotor activity, patterns of movement and exploration, startle reactivity, prepulse inhibition (PPI), and habituation in adult rats. METHODS: Male Sprague-Dawley rat pups (21 days old) were housed under enrichment (three per cage with toys and exposure to enriched environments), normal social (three per cage), or isolation (one per cage) conditions. Eight weeks later, locomotor and exploratory behaviors, acoustic startle reactivity, PPI, and habituation were measured in the three groups. RESULTS: Enrichment-reared rats exhibited reduced exploration and rapid habituation of locomotor activity, increased startle reactivity, and normal PPI and startle habituation compared with socially reared controls. Isolation-reared rats exhibited increased exploration and normal habituation of locomotor activity, increased startle reactivity, reduced PPI, and normal startle habituation. CONCLUSIONS: Isolation- and enrichment-reared rats exhibited opposite changes in some behaviors and similar changes in other behaviors. Specifically, rats raised in enriched conditions appear more efficient at assimilating stimuli from their environment than do rats reared in isolation. Nevertheless, both enrichment- and isolation-rearing conditions increased startle reactivity, whereas only isolation rearing led to disruptions of PPI in adulthood. These results suggest that isolation- and enrichment-rearing conditions produce some common and some differential effects on how rats process environmental stimuli. For studies of isolation-rearing effects on PPI, however, the complex and resource-intensive enrichment condition seems to offer few advantages over the normal social condition.

The genetic liability to stress and postweaning isolation have a competitive influence on behavioral organization in rats.

Rats housed in social isolation postweaning (isolates) show profound behavioral and neurobiological differences when compared to socially housed rats (socials). Fischer rats (F344) relative to Lewis rats are hyperresponsive and significantly more susceptible to stressful stimuli. This investigation tested the hypothesis that the behavioral effects of postweaning isolation are more pronounced in a strain of rats with high susceptibility to stress compared to a strain with low susceptibility to stress. Seventy male Sprague-Dawley, Lewis, and F344 rats were housed individually or in groups at weaning on Day 21 and tested on Day 85 in the Behavioral Pattern Monitor. There was no interaction between strain and postweaning isolation for measures of locomotor activity and exploratory behavior (holepoking). However, the postweaning isolation-induced increase in the frequency of repetitive straight movements, a measure of behavioral organization, was more pronounced in Lewis isolates compared to Sprague-Dawley and F344 isolates. These results do not support the hypothesis that rats with a higher susceptibility to stress show more pronounced changes in behavior following postweaning isolation; instead, increased susceptibility to stress may counteract the repetitive movement patterns induced by social isolation.