Browsing by Author "Potts, Geoffrey F."
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Item Disruption of executive attention in schizophrenia(2004) Wood, Susan McCullough; Potts, Geoffrey F.Disruption of attention is a hallmark symptom of schizophrenia, and event-related potentials have been instrumental in studying this deficit in these patients. Prior studies have shown consistent reduction of the auditory P300 in schizophrenia, while visual attention findings have been mixed. Both the auditory and visual N2b, an earlier, modality-specific attention index, are often reduced in schizophrenia, sometimes despite sparing of the visual P300. Thus there may be a dissociation between N2b and P300 attention effects in the auditory and visual modalities in schizophrenia. This study used auditory and visual oddball tasks and two bimodal tasks, each with a modality-specific target. Results showed that the N2b was differentially impacted in the patient group across modalities, while the P300 remained intact. This evidence suggests non-reduction of the P300 may be due to effortful compensation for deficits in the more vulnerable N2b component of stimulus classification in patients with schizophrenia.Item Exploring executive functions in children with attention deficit hyperactivity disorder using event related potentials(2006) Kothmann, Delia Katherine; Potts, Geoffrey F.Attention deficit hyperactivity disorder (ADHD) is a prevalent neurobehavioral disorder that affects individuals in early childhood and is characterized by cognitive impairments associated with executive functioning. However, the exact nature of the impairment(s) is/are unclear. In a recent meta-analysis, Miyake, Friedman, Emerson, Witzki, Howerter, and Wager (2000) demonstrated that there are at least three separable frontal executive functions: set switching, working memory updating, and response inhibition. Here we used event-related potentials (ERPs) to investigate whether the cognitive impairments seen in ADHD are specific to one of these executive functions or rather represent a global executive functioning deficiency. The current studies examined the time course and scalp localization of executive functions in Combined Type ADHD and in comparison control children by implementing modified versions of three executive tasks used by Miyake et al. (2000), local-global, tone-monitoring, and Stroop; versions more appropriate for the ADHD population. An additional non-executive task (visual oddball) was included in order to demonstrate that the deficits in ADHD are specific to executive functioning. The goal was to determine if children with ADHD perform differently on these three executive tasks and if this difference can be attributed to a deficit associated with one or more of the executive functions. The current findings show that ADHD impacts only a subset of cognitive operations in the executive functions, leaving the other ERPs in the executive tasks and the visual oddball unaffected. Specifically, the ADHD group was impaired on tasks involving allocation of attention and response inhibition, the cognitive operations most closely related to the diagnostic criteria for this subtype of ADHD. These findings may extend our knowledge of the time course and localization of executive functions and provide a tool for studying the nature of disrupted executive functioning in ADHD.Item Impulsivity and neural systems of rewards(2006) Martin, Laura E.; Potts, Geoffrey F.Behavioral studies of decision-making in impulsive individuals demonstrate biases for immediate rewards. Decision-making includes evaluating motivational values of both options and actions. In the current studies, event related potentials (ERPs) and functional magnetic imaging (fMRI) were used to assess the temporal and spatial properties of the ventral tegmental (VTA) dopamine (DA) reward system during item evaluation and action/outcome-monitoring in impulsivity. A passive reward evaluation and an active action/outcome-monitoring task were used to test a model predicting that dysregulation of the VTA DA reward system leads to overestimations of reward value in the prefrontal cortex and underestimations of punishments in the anterior cingulate cortex (ACC) during reward evaluation and action/outcome-monitoring respectively. Passive reward evaluation ERP results showed a prefrontal P2a ERP index of reward expectation that did not differ with impulsivity. FMRI reward evaluation results indicated that the basal ganglia and left superior frontal cortex were sensitive to rewarding outcomes, whereas the medial ACC was sensitive to non-rewarding outcomes. Left superior frontal cortex fMRI activation showed greater differentiation between better than expected and worse than expected outcomes among high impulsive participants. Action/outcome-monitoring ERP results showed an ERN ERP index the ACC in the action/outcome-monitoring with the greatest response on error trials that led to punishments. The ERN was also larger among high impulsives, compared to the low impulsives, when errors led to missed rewards. The fMRI results showed that the basal ganglia responded like the ERN to errors resulting in punishments. The ACC and right middle frontal regions showed greater activation to correct responses, and a right ACC region showed larger activations when correct responses led to rewards. However, these activations did not differ with impulsivity. In conclusion, the current results suggest differential responsiveness of the mesotelencephalic reward system in impulsive individuals which may lead to reward hypersensitivity but not punishment hyposensitivity during item evaluation and action/outcome-monitoring among high impulsive participants, as seen in the left superior frontal fMRI activation during item evaluation and in the ACC ERP activity during outcome-monitoring. Differences between the ERP and fMRI results may reflect the different physiological processes that give rise to the signals.Item Individual differences in decision-making and reward processing: An event-related potential investigation(2004) Martin, Laura E.; Potts, Geoffrey F.Gambling paradigms tapping both reward processing and decision-making tasks in control and patient populations have found differences in behavior based on individual differences in immediate reward representation. The current investigation examined decision-making in individuals who differed on self-reported measures of impulsivity and used event-related potentials (ERPs) to examine the network dynamics of reward and decision-making circuitry among low and high impulsive participants. An inferior frontal component, the anterior P2 (P2a), indexing orbitofrontal cortex (OFC) activity, and a medial frontal negativity (MFN), indexing anterior cingulate cortex (ACC) activity, were measured related to choices made from high-risk and low-risk decks of cards in two modified versions of the Iowa Gambling Task. Results indicated that the P2a indexed reward expectation in a single-presentation version of the Iowa Gambling Task and the MFN indexed evaluation of decisions in a dual-presentation version of the Iowa Gambling Task.