Self-focusing collapse distance in ultrashort pulses and measurement of nonlinear index.

We analyze the method of moving focus to determine the critical power for self-focusing by means of numerical simulation and a semianalytical model. It is shown that the original interpretation of a moving focus experiment does not hold in general and that inclusion of defocusing effects due to free electrons is necessary to relate the measured data to critical power.

Carotid body in the sudden infant death syndrome.

Sixty-three percent of victims of the sudden infant death syndrome had a subnormal volume and 23 percent an enlarged volume of glomic cells in their carotid bodies. Evidences of antecedent chronic alveolar hypoxia and hypoxemia were found in both groups but were more severe in the victims with enlarged glomic tissue.

Human amygdala sensitivity to the pupil size of others.

Stimulation of the amygdala produces pupil dilation in animal and human subjects. The present study examined whether the amygdala is sensitive to variations in the pupil size of others. Male subjects underwent event-related functional magnetic resonance imaging while passively viewing unfamiliar female faces whose pupils were either unaltered (natural variations in large and small pupils) or altered to be larger or smaller than their original size. Results revealed that the right amygdala and left amygdala/substantia innominata were sensitive to the pupil size of others, exhibiting increased activity for faces with relatively large pupils. Upon debrief, no subject reported being aware that the pupils had been manipulated. These results suggest a function for the amygdala in the detection of changes in pupil size, an index of arousal and/or interest on the part of a conspecific, even in the absence of explicit knowledge.

Response and habituation of the human amygdala during visual processing of facial expression.

We measured amygdala activity in human volunteers during rapid visual presentations of fearful, happy, and neutral faces using functional magnetic resonance imaging (fMRI). The first experiment involved a fixed order of conditions both within and across runs, while the second one used a fully counterbalanced order in addition to a low level baseline of simple visual stimuli. In both experiments, the amygdala was preferentially activated in response to fearful versus neutral faces. In the counterbalanced experiment, the amygdala also responded preferentially to happy versus neutral faces, suggesting a possible generalized response to emotionally valenced stimuli. Rapid habituation effects were prominent in both experiments. Thus, the human amygdala responds preferentially to emotionally valenced faces and rapidly habituates to them.

Amygdala response to fearful faces in anxious and depressed children.

BACKGROUND: Alterations in amygdala function have been implicated in the pathophysiological characteristics of adult anxiety and depressive disorders. Studies with healthy adults and children, as well as with adults who have amygdala lesions, have found facial expressions of emotion to be useful probes of amygdala activity. Our study examined the amygdala response to fearful and neutral facial expressions in healthy, anxious, and depressed children. We hypothesized that children with anxiety and depression may show atypical amygdala responses to emotional stimuli. METHODS: Twelve children (8-16 years of age) with generalized anxiety or panic disorder and 12 healthy comparison children underwent noninvasive functional magnetic resonance imaging while viewing photographs of fearful and neutral facial expressions. In a second comparison, 5 girls with major depressive disorder were compared with 5 anxious and 5 healthy girls from the previous sample. RESULTS: Children with anxiety disorders showed an exaggerated amygdala response to fearful faces compared with healthy children, whereas depressed children showed a blunted amygdala response to these faces. In addition, the magnitude of the amygdala's signal change between fearful and neutral faces was positively correlated with the severity of everyday anxiety symptoms. CONCLUSIONS: Our results suggest that amygdala function is affected in both anxiety and depression during childhood and adolescence. Moreover, this disruption appears to be specific to the child's own rating of everyday anxiety.

Amygdala response to facial expressions in children and adults.

BACKGROUND: The amygdala plays a central role in the human response to affective or emotionally charged stimuli, particularly fear-producing stimuli. We examined the specificity of the amygdala response to facial expressions in adults and children. METHODS: Six adults and 12 children were scanned in a 1.5-T scanner during passive viewing of fearful and neutral faces using an EPI BOLD sequence. All scans were registered to a reference brain, and analyses of variance were conducted on the pooled data to examine interactions with age and gender. RESULTS: Overall, we observed predominantly left amygdala and substantia innominata activity during the presentation of nonmasked fearful faces relative to fixation, and a decrease in activation in these regions with repeated exposure to the faces. Adults showed increased left amygdala activity for fearful faces relative to neutral faces. This pattern was not observed in the children who showed greater amygdala activity with neutral faces than with fearful faces. For the children, there was an interaction of gender and condition whereby boys but not girls showed less activity with repeated exposure to the fearful faces. CONCLUSIONS: This is the first study to examine developmental differences in the amygdala response to facial expressions using functional magnetic resonance imaging.

An fMRI study of anterior cingulate function in posttraumatic stress disorder.

BACKGROUND: Several recent neuroimaging studies have provided data consistent with functional abnormalities in anterior cingulate cortex in posttraumatic stress disorder (PTSD). In our study, we implemented a cognitive activation paradigm to test the functional integrity of anterior cingulate cortex in PTSD. METHODS: Eight Vietnam combat veterans with PTSD (PTSD Group) and eight Vietnam combat veterans without PTSD (non-PTSD Group) underwent functional magnetic resonance imaging (fMRI) while performing the Emotional Counting Stroop. In separate conditions, subjects counted the number of combat-related (Combat), generally negative (General Negative), and neutral (Neutral) words presented on a screen and pressed a button indicating their response. RESULTS: In the Combat versus General Negative comparison, the non-PTSD group exhibited significant fMRI blood oxygenation level-dependent signal increases in rostral anterior cingulate cortex, but the PTSD group did not. CONCLUSIONS: These findings suggest a diminished response in rostral anterior cingulate cortex in the presence of emotionally relevant stimuli in PTSD. We speculate that diminished recruitment of this region in PTSD may, in part, mediate symptoms such as distress and arousal upon exposure to reminders of trauma.

Exaggerated amygdala response to masked facial stimuli in posttraumatic stress disorder: a functional MRI study.

BACKGROUND: Converging lines of evidence have implicated the amygdala in the pathophysiology of posttraumatic stress disorder (PTSD). We previously developed a method for measuring automatic amygdala responses to general threat-related stimuli; in conjunction with functional magnetic resonance imaging, we used a passive viewing task involving masked presentations of human facial stimuli. METHODS: We applied this method to study veterans with PTSD and a comparison cohort of combat-exposed veterans without PTSD. RESULTS: The findings indicate that patients with PTSD exhibit exaggerated amygdala responses to masked-fearful versus masked-happy faces. CONCLUSIONS: Although some previous neuroimaging studies of PTSD have demonstrated amygdala recruitment in response to reminders of traumatic events, this represents the first evidence for exaggerated amygdala responses to general negative stimuli in PTSD. Furthermore, by using a probe that emphasizes automaticity, we provide initial evidence of amygdala hyperresponsivity dissociated from the "top-down" influences of medial frontal cortex.

Anterior cingulate cortex dysfunction in attention-deficit/hyperactivity disorder revealed by fMRI and the Counting Stroop.

BACKGROUND: The anterior cingulate cognitive division (ACcd) plays a central role in attentional processing by: 1) modulating stimulus selection (i.e., focusing attention) and/or 2) mediating response selection. We hypothesized that ACcd dysfunction might therefore contribute to producing core features of attention-deficit/hyperactivity disorder (ADHD), namely inattention and impulsivity. ADHD subjects have indeed shown performance deficits on the Color Stroop, an attentional/cognitive interference task known to recruit the ACcd. Recently, the Counting Stroop, a Stroop-variant specialized for functional magnetic resonance imaging (fMRI), produced ACcd activation in healthy adults. In the present fMRI study, the Counting Stroop was used to examine the functional integrity of the ACcd in ADHD. METHODS: Sixteen unmedicated adults from two groups (8 with ADHD and 8 matched control subjects) performed the Counting Stroop during fMRI. RESULTS: While both groups showed an interference effect, the ADHD group, in contrast to control subjects, failed to activate the ACcd during the Counting Stroop. Direct comparisons showed ACcd activity was significantly higher in the control group. ADHD subjects did activate a frontostriatal-insular network, indicating ACcd hypoactivity was not caused by globally poor neuronal responsiveness. CONCLUSIONS: The data support a hypothesized dysfunction of the ACcd in ADHD.

The emotional counting Stroop paradigm: a functional magnetic resonance imaging probe of the anterior cingulate affective division.

BACKGROUND: The emotional counting Stroop (ecStroop) functional magnetic resonance imaging (fMRI) activation paradigm was designed to recruit the anterior cingulate affective division (ACad). METHODS: Nine normal, healthy male and female subjects (mean age 24.2 years) reported via button press the number of neutral and negative words that appeared on a screen while reaction time and fMRI data were acquired. RESULTS: We observed a) greater ACad activation for negative versus neutral words during initial presentation blocks; b) lower overall ACad signal intensity during task performance (i.e., both negative and neutral words) compared to the baseline fixation condition; and c) no reaction time increase to negative versus neutral words. CONCLUSIONS: In a companion study of a cognitive version of the counting Stroop (Bush et al 1998), these same 9 subjects a) activated the more dorsal anterior cingulate cognitive division; b) also showed the overall decrease in ACad signal intensity; and c) demonstrated a reliable reaction time effect. Taken together, these data offer a within-group spatial dissociation of AC function based upon information content (i.e., cognitive vs. emotional) and/or presence of behavioral interference. We propose that the ecStroop will be a useful fMRI probe of ACad function in anxiety disorders.

Contributions of the amygdaloid central nucleus to the modulation of the nictitating membrane reflex in the rabbit.

The contributions of the amygdaloid central nucleus (ACe) to the modulation of the amplitude of the nictitating membrane reflex (NMR) were determined. Experiment 1 demonstrated that low-level electrical stimulation of the ACe enhances the amplitude of the NMR when administered immediately preceding the elicitation of the reflex by an eyelid stimulus. In Experiment 2 the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase determined that the ACe projects to the entire rostrocaudal extent of the lateral tegmental field (LTF), the brainstem area in which the multisynaptic component of the unconditioned NMR pathway is believed to be located. These results are consistent with the hypothesis that the ACe, via its projections to the LTF, modulates reflex sensitivity during conditioned arousal and may contribute to the associative enhancement of the unconditioned NMR that occurs early during Pavlovian nictitating membrane conditioning.

Effects of electrical stimulation of the amygdaloid central nucleus on neocortical arousal in the rabbit.

This study sought to determine whether electrical stimulation of the amygdaloid central nucleus (ACe) produces cholinergically mediated neocortical arousal manifested in the suppression of frontal cortex delta wave (1-4 Hz) activity. Stimulation in both anesthetized and conscious rabbits produced a suppression of delta activity that was accompanied by bradycardia and blocked by cholinergic antagonists. Stimulation of the adjacent putamen did not produce delta suppression, whereas stimulation of the adjacent ventral globus pallidus produced a suppression of shorter duration than that produced by ACe stimulation. The results suggest that the ACe influences neocortical arousal, which may be mediated by its influence on the activity of cholinergic neurons of the nucleus basalis.

Memory effect of DL-threo-3,4-dihydroxyphenylserine (DOPS) in human Korsakoff's disease.

A group of amnesic patients with Korsakoff's disease were treated with a single 1 g dose of DL-threo-3,4-dihydroxyphenylserine (DOPS) and placebo (lactose) in a double-blind crossover study. Three hours following administration, patients were given a battery of psychometric tests to determine the effects of the treatment on memory functions. Administration of DOPS had a significant effect on performance on the Memory Passages test but not on any of the other measures of memory. The effect of DOPS on Memory Passages is similar to the response observed following administration of clonidine in Korsakoff patients. Blood pressure and pulse, measured before and every 2 h after treatment, were unaffected by DOPS.

Thalamic deactivation during early implicit sequence learning: a functional MRI study.

Previous research has implicated the striatum in implicit sequence learning. However, imaging findings have been inconsistent with regard to activity within the thalamus during performance of such tasks. Contemporary models of cortico-striato-thalamic circuitry suggest opposing influences on thalamic activity; suppression of thalamic activity is mediated by the indirect pathway and enhancement is mediated by the direct pathway. Using functional magnetic resonance imaging, we studied activity within human thalamus during early and late phases of an implicit sequence learning task known to reliably recruit the striatum. Significant deactivation (decreased signal relative to a baseline condition) was observed within the thalamus during early implicit learning. This finding is consistent with models of cortico-striato-thalamic function and specifically supports a profile of early 'thalamic gating' via the indirect pathway.

Differential prefrontal cortex and amygdala habituation to repeatedly presented emotional stimuli.

Repeated presentations of emotional facial expressions were used to assess habituation in the human brain using fMRI. Significant fMRI signal decrement was present in the left dorsolateral prefrontal and premotor cortex, and right amygdala. Within the left prefrontal cortex greater habituation to happy vs fearful stimuli was evident, suggesting devotion of sustained neural resources for processing of threat vs safety signals. In the amygdala, significantly greater habituation was observed on the right compared to the left. In contrast, the left amygdala was significantly more activated than the right to the contrast of fear vs happy. We speculate that the right amygdala is part of a dynamic emotional stimulus detection system, while the left is specialized for sustained stimulus evaluations.

Differential response in the human amygdala to racial outgroup vs ingroup face stimuli.

Here we describe response in the human amygdala to the presentation of racial outgroup vs ingroup faces. Functional magnetic resonance imaging (fMRI) measures of brain activity were acquired while subjects who identified themselves as White or Black viewed photographs of both White and Black faces. Across all subjects, we observed significantly greater blood oxygen-level-dependent (BOLD) signal in the amygdala to outgroup vs ingroup faces, but only during later stimulus presentations. A region of interest (ROI)-based analysis of these voxels revealed a significant interaction between amygdala response to outgroup and ingroup faces over time. Specifically, the greater amygdala activation to outgroup faces during later stimulus presentations was the result of amygdala response habituation to repeated presentations of ingroup faces with sustained responses to outgroup faces. The present results suggest that amygdala responses to human face stimuli are affected by the relationship between the perceived race of the stimulus face and that of the subject. Results are discussed as consistent with a role for the amygdala in encoding socially and/or biologically relevant information. We conclude that researchers seeking to study brain responses to face stimuli in human subjects should consider the relationship between the race of subjects and stimuli as a significant potential source of variance. Moreover, these data provide a foundation for future related studies in the neuroscience of social cognition and race.

Probing striato-thalamic function in obsessive-compulsive disorder and Tourette syndrome using neuroimaging methods.

In summary, contemporary pathophysiological models of OCD and related disorders implicate CSTC circuitry. In this chapter, we have reviewed relevant concepts related to implicit learning and more specifically, the use of an implicit sequence learning paradigm as a probe of striato-thalamic function. An initial PET investigation of patients with OCD confirmed a priori hypotheses of failure to recruit right striatum, despite the absence of a performance deficit (22). A modified version of the SRT was studied in conjunction with fMRI and yielded reliable right-lateralized striatal activation in a cohort of 10 male subjects, with clear spatial dissociation of caudate and putamen activation foci (119). Subsequent studies in our laboratory suggest that this paradigm also yields a reliable temporal window of thalamic deactivation, and hence a means for assessing thalamic gating in human subjects (120). Finally, as presented in this chapter, preliminary data from the fMRI-SRT in patients with OCD and TS as well as normal control subjects appear to replicate and extend the findings from our original PET-SRT study in OCD. Future investigations in our laboratory will seek to elaborate upon these preliminary results. In particular, we intend to study psychiatric comparison groups to establish the generalizability and/or specificity of these findings across disorders. Within OCD, we hope to explore the relationship between abnormal brain-activation patterns and symptom dimensions (34). Further, by studying subjects with remitted OCD who have been successfully treated, we hope to determine whether the observed brain-activation abnormalities represent state or trait markers. Finally, we have already begun to test a hypothesis of parallel processing deficiency in OCD by using a dual-task version of the SRT that makes simultaneous demands on implicit and explicit information processing systems (128). It is our hope that this program of research will yield new insights about OCD and related disorders, including TS. Most importantly, as other teams of investigators pursue complementary lines of inquiry, it is our wish that collective efforts in this field will lead to improved diagnosis and treatment, if not cure or prevention, for those who are afflicted with these illnesses.

A functional MRI study of human amygdala responses to facial expressions of fear versus anger.

Functional magnetic resonance imaging (fMRI) of the human brain was used to compare changes in amygdala activity associated with viewing facial expressions of fear and anger. Pictures of human faces bearing expressions of fear or anger, as well as faces with neutral expressions, were presented to 8 healthy participants. The blood oxygen-level dependent (BOLD) fMRI signal within the dorsal amygdala was significantly greater to Fear versus Anger, in a direct contrast. Significant BOLD signal changes in the ventral amygdala were observed in contrasts of Fear versus Neutral expressions and, in a more spatially circumscribed region, to Anger versus Neutral expressions. Thus, activity in the amygdala is greater to fearful facial expressions when contrasted with either neutral or angry faces. Furthermore, directly contrasting fear with angry faces highlighted involvement of the dorsal amygdaloid region.

Inhibition of gene expression by ribozymes.

RNA enzymes, or ribozymes, can be defined as RNA molecules that promote a variety of reactions involving RNA and DNA molecules. These include site-specific cleavage, ligation, polymerization, and phosphoryl exchange (1). The use of ribozymes for medical therapy was recognized soon after RNA catalysis was discovered in the early 1980s (2). Three broad classes, naturally occurring ribozymes have been recognized: (1) RNase P, required for tRNA processing; (2) self-splicing introns, including group I and II introns of bacteria, mitochondria, and chloroplasts; and (3) selfcleaving viral agents, including hepatitis delta virus and components of plant viroids that cleave the RNA genome during replication. Because of their small size and great specificity, the self-cleaving ribozymes have the greatest potential for medical applications. The ability of these ribozymes to cleave other RNA molecules at specific sites makes them useful as inhibitors of viral replication or of cell proliferation (3-8).

Anticholesteremic property of Lactobacillus acidophilus yogurt fed to mature boars.

Three strains of Lactobacilus acidophilus (LA) were isolated from the feces of mature boars that were not being fed antibiotics from the Nebraska Gene Pool (NGP). All three LA isolates were screened in vitro for anticholesteremic and antimicrobial activities. One strain, LA16, caused the greatest reduction in cholesterol and inhibited both Bacillus subtilis and Escherichia coli the most. LA16 was used to produce 16, 18.9-liter quantities of acidophilus yogurt (AY), over a period of 8 wk, for use as a feed ingredient in diets for the NGP boars. Colony forming units (cfu), pH, protein, energy, Ca and P were consistent across all 16 batches of yogurt. All of the 18 boars were fed a high-cholesterol diet for a period of 56 d at a rate of 2.268 kg/(hd.d) to furnish 6.661 g/(hd.d) of cholesterol. Nine of the boars then were fed 1.81 kg/(hd.d) of a second diet that was supplemented with .454 kg/(hd.d) of AY. The other nine boars were fed the original diet. Cholesterol intake was the same for the two dietary treatments. Blood samples were collected weekly from the brachial-jugular region and the sera were analyzed for lipids. Acidophilus yogurt reduced serum cholesterol (P less than .01) and low density lipoproteins (P less than .08), but it had no effect on serum triglycerides (P greater than .23) or on high density lipoproteins (P greater than .11).