Priti I. Parekh

Regional brain activity when selecting a response despite interference: An H2 15O PET study of the stroop and an emotional stroop

The Stroop interference test requires a person to respond to specific elements of a stimulus while suppressing a competing response. Previous positron emission tomography (PET) work has shown increased activity in the right anterior cingulate gyrus during the Stroop test. It is unclear, however, whether the anterior cingulate participates more in the attentional rather than the response selection aspects of the task or whether different interference stimuli might activate different brain regions. We sought to determine (1) whether the Stroop interference task causes increased activation in the right anterior cingulate as previously reported, (2) whether this activation varied as a function of response time, (3) what brain regions were functionally linked to the cingulate during performance of the Stroop, and (4) whether a modified Stroop task involving emotionally distracting words would activate the cingulate and other limbic and paralimbic regions. Twenty‐one healthy volunteers were scanned with H215O PET while they performed the Stroop interference test (standard Stroop), a modified Stroop task using distracting words with sad emotional content (sad Stroop), and a control task of naming colors. These were presented in a manner designed to maximize the response selection aspects of the task. Images were stereotactically normalized and analyzed using statistical parametric mapping (SPM). Predictably, subjects were significantly slower during the standard Stroop than the sad Stroop or the control task. The left mideingulate region robustly activated during the standard Stroop compared to the control task. The sad Stroop activated this same region, but to a less significant degree. Correlational regional network analysis revealed an inverse relationship between activation in the left mideingulate and the left insula and temporal lobe. Additionally, activity in different regions of the cingulate gyrus correlated with performance speed during the standard Stroop. These results suggest that the left midcingulate is likely to be part of a neural network activated when one attempts to override a competing verbal response. Finally, the left midcingulate region appears to be functionally coupled to the left insula, temporal, and frontal cortex during cognitive interference tasks involving language. These results underscore the important role of the cingulate gyrus in selecting appropriate and suppressing inappropriate verbal responses.

Regional brain activity during transient self-induced anxiety and anger in healthy adults

BACKGROUND Several studies have demonstrated that transient self-induced sadness activates anterior paralimbic structures. To further examine the specificity of these findings and the neural substrates involved in anger and anxiety, we studied the neural correlates of the induction of anxiety and anger in healthy adults. METHODS We used H2(15)O and positron emission tomography (PET) to measure regional cerebral blood flow (rCBF) in 16 healthy adults during the induction of transient anxiety, anger, and neutral emotions. Subjects achieved differential emotions by recalling prior life events while viewing affect-appropriate faces. RESULTS Both the anxiety and anger conditions were associated with increased normalized rCBF in left inferior frontal and left temporal pole regions and decreased rCBF in right posterior temporal/parietal and right superior frontal cortex, compared to the neutral induction. Additionally, compared to neutral induction, anxiety was associated with increased rCBF in the left anterior cingulate and cuneus and decreased rCBF in right medial frontal cortex, while the anger induction was uniquely associated with increased rCBF in right temporal pole and thalamus. CONCLUSIONS Self-generated transient states of anxiety and anger are associated with both overlapping and distinct regional brain activity patterns and provide a template for further dissection of specific components of normal and pathologic emotions.

Gender differences in regional cerebral blood flow during transient self-induced sadness or happiness

Men, compared to women, are less likely to experience mood disorders. We wondered if gender differences exist in the ability to self-induce transient sadness and happiness, and in regional cerebral blood flow (rCBF) either at rest or during transient emotions. Ten adult men and 10 age-matched women, all healthy and never mentally ill, were scanned using H2(15)O positron emission tomography at rest and during happy, sad, and neutral states self-induced by recalling affect-appropriate life events and looking at happy, sad, or neutral human faces. At rest, women had decreased temporal and prefrontal cortex rCBF, and increased brainstem rCBF. There were no significant between-group differences in difficulty, effort required, or the degree of happiness or sadness induced. Women activated a significantly wider portion of their limbic system than did men during transient sadness, despite similar self-reported changes in mood. These findings may aid in understanding gender differences with respect to emotion and mood.

Anterior Paralimbic Mediation of Procaine-Induced Emotional and Psychosensory Experiences

BACKGROUND Procaine activates limbic structures in animals. In humans, acute intravenous administration of procaine yields emotional and psychosensory experiences and temporal lobe fast activity. We studied procaines acute effects on cerebral blood flow (CBF) in relationship to clinical responses. METHODS Cerebral blood flow was assessed by positron emission tomography with oxygen-15-labeled water in 32 healthy volunteers. Data were analyzed with statistical parametric mapping and magnetic resonance imaging-directed regions of interest. RESULTS Procaine increased global CBF and, to a greater extent, anterior paralimbic CBF. Subjects with intense procaine-induced fear compared with those with euphoria had greater increases in left amygdalar CBF. Absolute and normalized left amygdalar CBF changes tended to correlate positively with fear and negatively with euphoria intensity. Procaine-induced visual hallucinations appeared associated with greater global and occipital CBF increases. Absolute occipital CBF increases appeared to correlate positively with visual hallucination intensity. CONCLUSIONS Procaine increased anterior paralimbic CBF, and different clinical responses appeared to be associated with different patterns of CBF changes.

Relationships between thyroid hormone and antidepressant responses to total sleep deprivation in mood disorder patients

BACKGROUND Acute transient antidepressant effects of sleep deprivation are consistently observed in 50% of depressed patients, but the mechanisms of these, at times, dramatic improvements in mood have not been adequately elucidated. Some, but not all, studies suggest a relationship to increased thyroid-stimulating hormone (TSH) secretion. METHODS TSH and other thyroid indices were measured at 8:00 AM after a baseline nights sleep and at 8:00 AM following a night of total sleep deprivation (S.D.) in 34 medication-free, affective disorder patients assessed with Hamilton, Beck, and Bunney-Hamburg depression ratings as well as two hourly self-ratings on a visual analog scale. RESULTS Compared with baseline, S.D. induced highly significant increases in TSH, levothyroxine, free levothyroxine, and triiodothyronine. The 12 S.D. responders tended to have greater TSH increases than the 15 nonresponders (p < .10). The change in Beck depression ratings significantly correlated with the change in TSH (r = -.40, p = .0496, n = 24). CONCLUSIONS These data are consistent with several other reports of a significant relationship between degree of antidepressant response to S.D. and increases in TSH measured at 8:00 AM near their usual nadir. Acute removal of the sleep-related break on the hypothalamic-pituitary-thyroid axis remains a promising candidate for the mechanism of sleep deprivation-induced improvement in mood in depressed patients.

Procaine-induced increases in limbic rCBF correlate positively with increases in occipital and temporal EEG fast activity.

SummaryPrevious independent EEG and PET studies suggest that administration of intravenous procaine hydrochloride selectively activates limbic brain structures. To further elucidate procaines effects and explore the relationship between quantitative EEG (qEEG) and regional cerebral blood flow (rCBF), we simultaneously recorded qEEG and sampled rCBF using O-15 water PET in 20 healthy volunteers during single-blind injections of saline (baseline condition) followed by intravenous procaine (1.84 mg/kg). After thorough screening of EEG records, a subgroup of 7 subjects with EEG data relatively free of both muscle and movement artifacts was selected for analysis. Quantitative spectral EEG data from right occipital and temporal leads were then correlated with each subjects PET rCBF values on a pixel by pixel basis, both at baseline and after procaine. The most striking finding was that the increases in occipital and temporal omega activity from baseline to procaine positively correlated with rCBF increases in the amygdala and its efferents (p<.05), in a pattern very similar to the rCBF increases seen after procaine administration. This suggests that omega activity may reflect activation of deeper brain limbic structures. Also, the convergence of EEG and PET data further supports procaines selective limbic activation.