The impact of the posterior parietal and dorsolateral prefrontal cortices on the optimization of long-term versus immediate value.

fMRI research suggests that both the posterior parietal cortex (PPC) and dorsolateral prefrontal cortex (DLPFC) help individuals select better long-term monetary gains during intertemporal choice. Previous neuromodulation research has demonstrated that disruption of the DLPFC interferes with this ability. However, it is unclear whether the PPC performs a similarly important function during intertemporal choice, and whether the functions performed by either region impact choices involving losses. In the current study, we used low-frequency repetitive transcranial magnetic stimulation to examine whether the PPC and DLPFC both normally facilitate selection of gains and losses with better long-term value than alternatives during intertemporal choice. We found that disruption of either region in the right hemisphere led to greater selection of both gains and losses that had better immediate, but worse long-term value than alternatives. This indicates that activity in both regions helps individuals optimize long-term value relative to immediate value in general, rather than being specific to choices involving gains. However, there were slightly different patterns of effects following disruption of the right PPC and right DLPFC, suggesting that each region may perform somewhat different functions that help optimize choice.

An fMRI examination of visual integration in schizophrenia.

Behavioral and electrophysiological studies of schizophrenia have consistently demonstrated impairments in the integration of visual features into unified perceptual representations. Specific brain regions involved in this dysfunction, however, remain to be clarified. This study used functional Magnetic Resonance Imaging (fMRI) to examine the relative involvement of visual cortex areas (involved in form perception) and parietal and frontal regions (involved in attention), in the visual integration impairment in schizophrenia. Fourteen patients with schizophrenia and 14 healthy controls were compared on behavioral performance and data acquired via fMRI while completing a contour integration task that had previously been used to identify a visual integration deficit in schizophrenia. The schizophrenia patients demonstrated poorer visual integration than controls. Analyses of peak signal change indicated that while the groups were equivalent in area V1, the schizophrenia group demonstrated reduced signal in areas V2-V4, which are the earliest regions sensitive to global configurations of stimuli. Moreover, whereas the control group demonstrated greater recruitment of prefrontal and parietal areas during perception of integrated forms compared to random stimuli, the schizophrenia group demonstrated greater recruitment of frontal regions during perception of random stimuli. The two groups differed on brain regions involved in form perception even when they were matched on accuracy levels. The visual integration disturbance in schizophrenia involves both deficient basic visual processes (beginning as early as occipital region V2), as well as reduced feedback from visual attention regions that normally serves to amplify relevant visual representations relative to irrelevant information.

Perceptual organization in first episode schizophrenia and ultra-high-risk states.

Deficits in perceptual organization have been consistently reported in schizophrenia, as has an association between these deficits, disorganized symptoms, and poorer premorbid functioning and prognosis, suggesting that they may be an index of illness severity or progression. It is unclear, however, whether the impairment is present at, or before the first psychotic episode. This study examined perceptual organization in young people considered to be at high-risk for schizophrenia, defined by the "close-in" strategy [Yung, A.R., McGorry, P.D., McFarlane, C.A., Jackson, H.J., Patton, G.C., Rakkar, 1996. Monitoring and care of young people at incipient risk of psychosis. Schizophrenia Bulletin, 22, 283-303]. The high-risk group (n=70) was compared to first-episode patients (n=54), and nonpatients (n=24) using a task with known sensitivity to perceptual organization deficits in schizophrenia, and whose scores have predicted long-term outcome and disorganized symptomatology in past studies [Knight, R.A., Silverstein, S.M., 1998. The role of cognitive psychology in guiding research on cognitive deficits in schizophrenia. In Lenzenweger, M., Dworkin, R.H., (Eds.), Origins and Development of Schizophrenia: Advances in Experimental Psychopathology. APA Press, Washington DC, pp. 247-295.; Silverstein, S.M., Knight, R.A., Schwarzkopf, S.B., West, L.L., Osborn, L.M. Kamin, D., 1996b. Stimulus configuration and context effects in perceptual organization in schizophrenia. Journal of Abnormal Psychology 105, 410-420.; Silverstein, S.M., Schenkel, L.S., Valone, C., Nuernberger, S., 1998a. Cognitive deficits and psychiatric rehabilitation outcomes in schizophrenia. Psychiatric Quarterly 69, 169-191.; Silverstein, S.M., Bakshi, S., Chapman, R.M., Nowlis, G., 1998b. Perceptual organization of configural and nonconfigural visual patterns in schizophrenia: effects of repeated exposure. Cognitive Neuropsychiatry 3, 209-223]. There were no differences between groups, and the first-episode group demonstrated non-significantly more sensitivity to stimulus organization than the other groups. When the high-risk group was broken down into its 3 subgroups (A--family history of psychotic illness and recent drop of 30+ points in the GAF scale; B--history of attenuated psychotic symptoms; C--brief limited intermittent psychotic symptoms), only group A demonstrated evidence of impairment, but this group differed significantly only from first- and young, later-episode schizophrenia patients, not from nonpatients. These findings are consistent with recent data on pre-attentive processes in schizophrenia which indicate that performance is not impaired and may even be enhanced, early in the illness, with dysfunctions beginning with increased chronicity.

The Balloon Analog Insurance Task (BAIT): a behavioral measure of protective risk management.

Prior methods used to assess individual differences related to risk have not focused on an important component of risk management: how willing individuals are to pay for or take actions to insure what they already have. It is not clear whether this type of protective risk management taps into the same individual differences as does risk taking propensity measured by existing risk taking tasks. We developed a novel task to assess protective risk management, the Balloon Analog Insurance Task (BAIT), which is modeled after the Balloon Analog Risk Task (BART). In the BAIT, individuals are forced to decide how much money they are willing to pay in order to insure a specific fraction of their prior winnings given changing but imprecise levels of risk of monetary loss. Participants completed the BART and BAIT for real monetary rewards, and completed six self report questionnaires. The amount of insurance purchased on the BAIT was positively correlated with scores on the Intolerance of Uncertainty Scale and on the Checking scale of the revised Obsessive Compulsive Inventory. Conversely, the amount of insurance purchased was negatively correlated with scores on the Domain Specific Risk Taking Questionnaire, and on the Psychopathic Personality Inventory (PPI). Furthermore, relationships between insurance purchased and these scales remained significant after controlling for the BART in linear regression analyses, and the BART was only a significant predictor for measures on one scale--the PPI. Our results reveal that behavior on the BAIT taps into a number of individual differences that are not related to behavior on another measure of risk taking. We propose that the BAIT may provide a useful complement to the BART in the assessment of risk management style.

Perceptual organization and visual search processes during target detection task performance in schizophrenia, as revealed by fMRI.

BACKGROUND: Past studies of perceptual organization in schizophrenia have demonstrated impairments binding fragmented stimulus components into unified representations. ERP and fMRI data indicate that even under conditions of adequate behavioral task performance, significant and meaningful changes in cortical and subcortical activation are present. Here, we examined, using fMRI, activation differences on a visual task wherein feature grouping was a precursor to the formation of distinct groups in the service of target location and identification. METHOD: Fourteen schizophrenia patients and 16 healthy controls completed a target detection task with 2 conditions: one in which target-distractor grouping facilitates detection (the Isolated condition) and one in which it hinders detection (the Embedded condition). Stimuli were blocked by condition. Accuracy and RT data were obtained in addition to fMRI data. RESULTS: Patients and controls did not differ significantly in accuracy or RT in either condition. Within this context, controls demonstrated greater recruitment of brain regions involved in visual-spatial processing, and the groups differed in activity in areas known to support visual search, visual analysis, decision making and response generation. CONCLUSION: These findings are consistent with past data indicating reduced processing of stimulus organization, and the subsequent use of inefficient visual search strategies, even under conditions when behavioral performance is at a high level and matches that of healthy controls.