Geoffrey F. Potts

When Things Are Better or Worse than Expected: The Medial Frontal Cortex and the Allocation of Processing Resources

Access to limited-capacity neural systems of cognitive control must be restricted to the most relevant information. How the brain identifies and selects items for preferential processing is not fully understood. Anatomical models often place the selection mechanism in the medial frontal cortex (MFC), and one computational model proposes that the mesotelencephalic dopamine (DA) system, via its reward prediction properties, provides a gate through which information gains access to limited-capacity systems. There is a medial frontal event-related potential (ERP) index of attention selection, the anterior positivity (P2a), associated with DA reward system input to the MFC for the identification of task-relevant perceptual representations. The P2a has a similar spatio-temporal distribution as the medial frontal negativity (MFN), elicited to error responses or choices resulting in monetary loss. The MFN has also been linked to DA projections to the MFC but for action monitoring rather than attention selection. This study proposes that the P2a and the MFN reflect the same MFC evaluation function and use a passive reward prediction design containing neither instructed attention nor response to demonstrate that the ERP over medial frontal leads at the P2a/MFN latency is consistent with activity of midbrain DA neurons, positive to unpredicted rewards and negative when a predicted reward is withheld. This result suggests that MFC activity is regulated by DA reward system input and may function to identify items or actions that exceed or fail to meet motivational prediction.

An ERP index of task relevance evaluation of visual stimuli

Recently several event-related potential attention studies have described a prefrontal positivity at about the same latency as the posterior N2 (approximately 200-300 ms), variously termed the frontal selection positivity (FSP), the anterior P2 (P2a), or the frontal P3 (P3f). These components have a similar spatio-temporal distribution and similar eliciting properties, suggesting that they represent the same component. However, these components have been differentially interpreted as arising from neural systems of feature selection, stimulus evaluation, or response production. The present study employed a visual target detection (oddball) design with different response conditions: passive (no response), overt (keypress), and covert (silent count), to examine the impact of task relevance and response production on the frontal P2a. The results showed that the P2a was present to task-relevant stimuli but had the same scalp topography and estimated source-dipole locations in both overt and covert responding, indicative of an index of stimulus evaluation, rather than response production.

Frontal evaluation and posterior representation in target detection.

This study examined the topography of the event-related potential in visual-spatial compared to visual-object target detection. The initial index of target detection in the ERP was an inferior anterior P2a accompanied by a posterior N2b. Single unit studies in the monkey indicate that the detection of task-relevant stimuli requires interaction between prefrontal cortex and perceptual representation areas in the posterior brain. The posterior brain processes the physical features of stimuli while frontal cortex performs higher-order operations, such as evaluating the task-relevance of a stimulus. Target detection requires an interaction between feature representations and relevance representations. We hypothesize that the P2a and N2b ERP indices of target detection reflect this frontal/posterior interaction. Visual-spatial feature information is processed in the dorsal posterior brain (posterior parietal cortex) and visual-object information is processed in the ventral posterior brain (inferior occipito-temporal cortex). We observed that at the peak of the P2a the N2b was located over posterior dorsal leads in visual-spatial target detection and over posterior ventral leads in visual-object target detection. The P2a was largest over inferior prefrontal leads in both tasks. We suggest that this distribution is consistent with interaction between orbitofrontal cortical areas of salience representation and posterior cortical areas of stimulus feature representation.

Frontal and inferior temporal cortical activity in visual target detection: Evidence from high spatially sampled event-related potentials

SummaryVisual event-related potential (ERP) studies show effects due to target detection in the P3 and in earlier negativities over posterior recording sites. The topography of these earlier components suggests contributions from both anterior and posterior neural generators, however these studies were performed with sparse recording arrays and may not have provided a full description of the scalp topography of the visual ERP. The current study employed a high-density recording array (64 channels) and spherical spline interpolated topographic voltage and current density maps to describe the scalp distribution of the major deflections in the visual ERP from a visual oddball paradigm: the P1, N1, N2/P2a (a temporally coincident posterior negativity and anterior positivity) and P3. A modified difference wave analysis was also performed to track the time-course of target detection effects in the ERP. Target detection effects were found in the N2/P2a and P3 components. The scalp distribution of the N2/P2a was consistent with separate frontal and posterior neural generators and this is discussed in reference to human hemodynamic and nonhuman primate studies of neural activity in the inferior temporal visual object recognition system and in frontal systems of selective attention and working memory in visual target detection tasks.

Reduced punishment sensitivity in neural systems of behavior monitoring in impulsive individuals.

This study measured the response-locked event-related potential during a flanker task with performance-based monetarily rewarding and punishing trials in 37 undergraduate students separated into high- and low-impulsive groups based on a median split on self-reported Barrett Impulsiveness Scale. The high-impulsive group had a smaller medial frontal error-related negativity (ERN) on punishment trials than the low-impulsive group. The medial prefrontal neural system of behavior monitoring, indexed by the ERN, appears less sensitive to punishment signals in normal impulsivity. This reduced punishment sensitivity in impulsivity, a personality variation associated with several mental and personality disorders including ADHD and substance abuse may be related to the tendency to select short-term rewards despite potential long-term negative consequences in these individuals.

Identification of neural circuits underlying P300 abnormalities in schizophrenia

Event-related potentials (ERPs) provide a noninvasive method to evaluate neural activation and cognitive processes in schizophrenia. The pathophysiological significance of these findings would be greatly enhanced if scalp-recorded ERP abnormalities could be related to specific neural circuits and/or regions of the brain. Using quantitative approaches in which scalp-recorded ERP components are correlated with underlying neuroanatomy in schizophrenia, we focused on biophysical and statistical procedures (partial least squares) to relate the auditory P300 component to anatomic measures obtained from quantitative magnetic resonance imaging. These findings are consistent with other evidence that temporal lobe structures contribute to the generation of the scalp-recorded P300 component and that P300 amplitude asymmetry over temporal recording sites on the scalp may reflect anatomic asymmetries in the volume of the superior temporal gyrus in schizophrenia.

Sex-related ERP differences in deviance detection

The effect of sex on neural mechanisms of auditory mismatch detection was examined using dense sensor array (128 channel) event-related potential recordings (ERPs). ERPs of 32 right-handed subjects (16 males) were recorded to frequent (85%, 880 Hz) and infrequent (15%, 1480 Hz) tones. There were no sex differences in mismatch negativity (80-180 ms), however, the fronto-central P2 (180-260 ms) was less positive in males (F=12.56, P<0.005) and the N2 (260-340 ms) was more negative in males (F=6.28, P<0.05). The increased negativity in males spanning the P2 and N2 may index a top-down process of attention bias towards novelty. This result supports the hypothesis of an adaptive, sexually dimorphic processing of novel events in humans.

Electrophysiological and Hemodynamic Responses to Reward Prediction Violation

Anterior cingulate cortex has been functionally linked to the detection of outcomes that are worse than expected using both scalp electrophysiological [event-related potential (ERP)] and hemodynamic [functional MRI (fMRI)] responses. This study used a reward prediction violation design which acquired both ERP and fMRI data from the same participants in different sessions. Both the medial frontal negativity (MFN) ERP response and anterior cingulate cortex hemodynamic activity differentiated between reward delivery and expectation with the largest MFN and anterior cingulate cortex response when predicted rewards were not delivered. Inverse modeling placed the MFN source near the anterior cingulate cortex hemodynamic activation. The fMRI study also showed increased striatal response to rewards regardless of prediction indicating dissociation of neural processing of reward and reward expectation.

Effects of dialect on merger perception: ERP and behavioral correlates

Native speakers of a language are often unable to consciously perceive, and have altered neural responses to, phonemic contrasts not present in their language. This study examined whether speakers of dialects of the same language with different phoneme inventories also show measurably different neural responses to contrasts not present in their dialect. Speakers with (n=11) and without (n=11) an American English I/E (pin/pen) vowel merger in speech production were asked to discriminate perceptually between minimal pairs of words that contrasted in the critical vowel merger and minimal pairs of control words while their event-related potential (ERPs) were recorded. Compared with unmerged dialect speakers, merged dialect speakers were less able to make behavioral discriminations and exhibited a reduced late positive ERP component (LPC) effect to incongruent merger vowel stimuli. These results indicate that between dialects of a single language, the behavioral response differences may reflect neural differences related to conscious phonological decision processes.

Preliminary feasibility and efficacy of a brief motivational intervention with psychophysiological feedback for cocaine abuse

Abstract Motivational interviewing (MI) with personalized feedback, particularly related to biological markers of risk or harm, has been found effective for alcohol use disorders, but has not been fully investigated in cocaine use disorders. A randomized, controlled pilot study evaluating the feasibility and preliminary efficacy of a brief MI intervention using EEG/ERP graphical feedback for cocaine abusers was conducted. Treatment-seeking cocaine abusers (N = 31) were randomly assigned to a two-session MI intervention or a minimal control condition. All participants received EEG assessments at intake and post-treatment. Results indicated that the MI intervention was feasible and the subjective impact of the EEG feedback was positive. Significant group differences in percentage of cocaine positive urine screens across the study were found, favoring the MI group; 84.9% for the control group and 62.6% in the MI group, p > .05. Further research must determine the specific conditions under which MI is most appropriate and efficacious.