L. Forest Gruss

Aversive learning shapes neuronal orientation tuning in human visual cortex

The responses of sensory cortical neurons are shaped by experience. As a result perceptual biases evolve, selectively facilitating the detection and identification of sensory events that are relevant for adaptive behaviour. Here we examine the involvement of human visual cortex in the formation of learned perceptual biases. We use classical aversive conditioning to associate one out of a series of oriented gratings with a noxious sound stimulus. After as few as two grating-sound pairings, visual cortical responses to the sound-paired grating show selective amplification. Furthermore, as learning progresses, responses to the orientations with greatest similarity to the sound-paired grating are increasingly suppressed, suggesting inhibitory interactions between orientation-selective neuronal populations. Changes in cortical connectivity between occipital and fronto-temporal regions mirror the changes in visuo-cortical response amplitudes. These findings suggest that short-term behaviourally driven retuning of human visual cortical neurons involves distal top–down projections as well as local inhibitory interactions.

Face-evoked steady-state visual potentials: effects of presentation rate and face inversion

Face processing can be explored using electrophysiological methods. Research with event-related potentials has demonstrated the so-called face inversion effect, in which the N170 component is enhanced in amplitude and latency to inverted, compared to upright, faces. The present study explored the extent to which repetitive lower-level visual cortical engagement, reflected in flicker steady-state visual evoked potentials (ssVEPs), shows similar amplitude enhancement to face inversion. We also asked if inversion-related ssVEP modulation would be dependent on the stimulation rate at which upright and inverted faces were flickered. To this end, multiple tagging frequencies were used (5, 10, 15, and 20 Hz) across two studies (n = 21, n = 18). Results showed that amplitude enhancement of the ssVEP for inverted faces was found solely at higher stimulation frequencies (15 and 20 Hz). By contrast, lower frequency ssVEPs did not show this inversion effect. These findings suggest that stimulation frequency affects the sensitivity of ssVEPs to face inversion.

Affective Learning and Psychophysiological Reactivity in Dementia Patients

We examined the association of faces with biographical information that varied in emotional content in patients with Alzheimers disease and a healthy control group. During two experimental sessions, participants rated neutral male faces on dimensions of hedonic valence and emotional arousal, later paired with fictitious biographical information. Both groups changed their ratings of the faces according to the biographical content. Free recall and recognition were tested in the second session. Patients neither recalled the biographical information nor recognized the faces, whereas the controls did. In addition, psychophysiological measures were taken in response to the face stimuli. Patients showed significant heart rate modulation as a function of their emotion ratings, whereas the controls did not. No correlation of rating changes with skin conductance was found in any group. Results suggest that psychophysiological reactions such as heart rate changes may indicate preserved affective associative learning in dementia patients despite impaired explicit memory.

Multimodal Imaging Evidence for a Frontoparietal Modulation of Visual Cortex during the Selective Processing of Conditioned Threat

Emotionally salient cues are detected more readily, remembered better, and evoke greater visual cortical responses compared with neutral stimuli. The current study used concurrent EEG-fMRI recordings to identify large-scale network interactions involved in the amplification of visual cortical activity when viewing aversively conditioned cues. To generate a continuous neural signal from pericalcarine visual cortex, we presented rhythmic (10/sec) phase-reversing gratings, the orientation of which predicted the presence (CS+) or absence (CS−) of a cutaneous electric shock (i.e., the unconditioned stimulus). The resulting single trial steady-state visual evoked potential (ssVEP) amplitude was regressed against the whole-brain BOLD signal, resulting in a measure of ssVEP-BOLD coupling. Across all trial types, ssVEP-BOLD coupling was observed in both primary and extended visual cortical regions, the rolandic operculum, as well as the thalamus and bilateral hippocampus. For CS+ relative to CS− trials during the conditioning phase, BOLD-alone analyses showed CS+ enhancement at the occipital pole, superior temporal sulci, and the anterior insula bilaterally, whereas ssVEP-BOLD coupling was greater in the pericalcarine cortex, inferior parietal cortex, and middle frontal gyrus. Dynamic causal modeling analyses supported connectivity models in which heightened activity in pericalcarine cortex for threat (CS+) arises from cortico-cortical top–down modulation, specifically from the middle frontal gyrus. No evidence was observed for selective pericalcarine modulation by deep cortical structures such as the amygdala or anterior insula, suggesting that the heightened engagement of pericalcarine cortex for threat stimuli is mediated by cortical structures that constitute key nodes of canonical attention networks.

The role of the COMT val158met polymorphism in mediating aversive learning in visual cortex

The catechol-O-methyltransferase (COMT) val158met single nucleotide polymorphism (SNP) alters metabolic activity of the COMT enzyme regulating catecholamines, with the Val (valine) allele resulting in 40% greater enzymatic activity than the Met (methionine) allele. Previous research has identified systematic inter-individual differences in cognitive and behavioral phenotypes related to this polymorphism, often attributed to the fact that extracellular dopamine in the prefrontal cortex is strongly affected by the COMT enzyme. The neurophysiological mechanisms mediating these inter-individual differences in specific brain systems and task contexts remain to be established however. In the current study, we examined the extent to which physio-mechanistic differences by COMT genotype affect somato-visceral and visual cortical responses to learned threat cues. Classical aversive differential conditioning was implemented using rapidly phase-reversing grating stimuli, previously shown to engage retinotopic visual cortex. Differential response patterns in sensory and autonomic systems were elicited by pairing one grating (CS+, conditioned stimulus), but not the other (CS-), with a noxious stimulus. Dense-array electroencephalography and somato-visceral measures of defensive reactivity were recorded in addition to self-report data. Individuals of the Val/Val genotype, compared to Met allele carriers, reliably showed greater initial enhancement in their visuocortical response to the CS+, accompanied by stronger defensive engagement, indexed by heart rate acceleration and startle potentiation. The finding that COMT polymorphism status affects threat cue reactivity at the visuocortical level is consistent with the notion that sensory processing of threat is facilitated by strong re-entrant bias signals from anterior areas, including the prefrontal cortex.

Disclosure of Diagnosis in Early Recognition of Psychosis

Abstract There is a debate concerning risks and benefits of early intervention in psychosis, especially concerning diagnosis disclosure. The present study reports preliminary findings on self-reported locus of control and psychological distress after the disclosure of diagnosis in an early recognition center. We compared the ratings of the locus of control and psychological distress before and after communication of diagnosis. The study included individuals with an at-risk mental state (ARMS) (n = 10), schizophrenia (n = 9), and other psychiatric disorders (n = 11). Results indicate greater endorsement of the internal locus of control in individuals with ARMS after communication of diagnosis in contrast to the other groups. Our results suggest that disclosure of diagnosis in an early recognition center leads to a reduction of psychological distress and increased feelings of control over ones health. Persons with ARMS seem to particularly benefit from disclosure of diagnosis as part of early intervention.

Relating BOLD and ssVEPs during visual aversive conditioning using concurrent EEG-fMRI recordings

Functional and electrophysiological measures indicate visual cortical responses evoked by emotionally arousing versus neutral stimuli are amplified, a process thought to be mediated by re-entrant projections from anterior cortical and subcortical structures. In healthy human observers, neuroimaging techniques with high temporal and spatial resolution are necessary to test such hypotheses. Here, blood-oxygen level dependent (BOLD) data and EEG data were collected simultaneously during a classical conditioning paradigm in which the orientation of grating stimuli (the conditioned stimuli, CS) predicted the presence/absence of a cutaneous electric shock (i.e., the unconditioned stimulus). Gratings were phase-reversed for a duration of 5 seconds, at a fixed rate (10/sec), evoking steady-state visual evoked brain potentials (ssVEP). In addition to considering the ssVEP and fMRI data separately, electrophysiological indices of single-trial visual engagement were extracted from ssVEP data and used to construct a predictive model for BOLD activation. BOLD and ssVEP data converged to show specific engagement of circumscribed areas in the calcarine fissure and occipital pole, in response to the phase reversal. Across experimental phases, BOLD in regions such as middle-temporal cortex, anterior insular cortex, and frontal cortical regions related to trial-by-trial fluctuations in ssVEP amplitude. Meeting abstract presented at VSS 2015.

What does the dot-probe task measure? A reverse correlation analysis of electrocortical activity

The dot-probe task is considered a gold standard for assessing the intrinsic attentive selection of one of two lateralized visual cues, measured by the response time to a subsequent, lateralized response probe. However, this task has recently been associated with poor reliability and conflicting results. To resolve these discrepancies, we tested the underlying assumption of the dot-probe task-that fast probe responses index heightened cue selection-using an electrophysiological measure of selective attention. Specifically, we used a reverse correlation approach in combination with frequency-tagged steady-state visual potentials (ssVEPs). Twenty-one participants completed a modified dot-probe task in which each member of a pair of lateralized face cues, varying in emotional expression (angry-angry, neutral-angry, neutral-neutral), flickered at one of two frequencies (15 or 20 Hz), to evoke ssVEPs. One cue was then replaced by a response probe, and participants indicated the probe orientation (0° or 90°). We analyzed the ssVEP evoked by the cues as a function of response speed to the subsequent probe (i.e., a reverse correlation analysis). Electrophysiological measures of cue processing varied with probe hemifield location: Faster responses to left probes were associated with weak amplification of the preceding left cue, apparent only in a median split analysis. By contrast, faster responses to right probes were systematically and parametrically predicted by diminished visuocortical selection of the preceding right cue. Together, these findings highlight the poor validity of the dot-probe task, in terms of quantifying intrinsic, nondirected attentive selection irrespective of probe/cue location.

Visuocortical changes during discriminant aversive conditioning: Effects of inter-individual differences in contingency awareness and autonomic engagement

Contingency learning of a noxious stimulus can be systematically studied in humans using classical fear conditioning. Conditioning studies utilizing the steady state visually evoked potential (ssVEP) have shown CS discrimination to occur as far downstream as lower-tier visual cortex, but the temporal evolution and inter-individual differences contributing to this process remain unclear. We implemented an uninstructed, differential fear-conditioning paradigm in which two orientations of a rapidly phase-reversing Gabor grating served as the conditioned stimuli (CS), only one of which (CS+) was ever paired with a 96db white noise (US, unconditioned stimulus). After a brief habituation phase, participants (n=20) were informed that a loud noise would occur at the end of some trials and were asked after every trial to indicate the likelihood of hearing the loud noise when viewing a specific Gabor grating. Acquisition consisted of an initial 100% CS+/US contingency followed by partial pairing (66%) and one re-exposure trial presented halfway through extinction. Preliminary results indicate that one group of participants (n=11) demonstrated rapid and sustained CS discrimination in their contingency ratings lasting throughout extinction, whereas the other group (n=9) showed gradual or no discrimination during acquisition. In terms of ssVEP data, observers with rapid and sustained discrimination learning demonstrated strong selective amplification of the CS+ grating, which habituated late in acquisition. By contrast, observers with little behavioral discrimination displayed later and smaller discrimination effects at the level of visual cortex. This suggests that behavioral responses to the conditioning regime are reflected in temporal dynamics of visual electrocortical facilitation. Meeting abstract presented at VSS 2015.