Hemispheric Asymmetry in Conditioning to Facial Emotional Expressions

In the present experiment, we report a right hemisphere advantage for autonomic conditioning to facial emotional expressions. Specifically, angry, but not happy, facial expressions showed significantly more resistance to extinction when presented initially to the right as compared to the left hemisphere. Slides of happy and angry faces were used as conditioned stimuli (CS+ and CS-) with shock as the unconditioned stimulus (UCS). Half of the subjects (n = 15) had the angry face as CS+ (and the happy face as CS-), the other half had the happy face as CS+ (and the angry face as CS-). During acquisition, the CSs were presented foveally. During extinction, using the Visual Half-Field (VHF) technique, half of the CS+ and CS- trials were randomly presented in the right visual half-field (initially to the left hemisphere), and half of the trials were presented in the left half-field (initially to the right hemisphere). Stimuli were presented for 210 ms during acquisition, and for 30 ms during extinction. Bilateral skin conductance responses (SCRs) were recorded. The results showed effects of acquisition only for the angry CS+ group. During extinction, there was a significant Conditioning X Half-field interaction which was due to greater SCRs to the CS+ angry face when it was presented in the left half-field. It is concluded that the present results reveal hemisphere asymmetry effects in facial emotional conditioning.     

Hemispheric Asymmetry and Human Electrodermal Conditioning: The Dichotic Extinction Paradigm

It was hypothesized that classically conditioned responses to an auditory verbal CS initially presented only to the left cerebral hemisphere would be greater than when the same CS was presented to the right hemisphere. The experiment consisted of three different phases in a dichotic extinction paradigm. During the habituation phase the CS+ and CS? were presented binaurally, and separated. All subjects were treated alike. During the acquisition phase the conditioning subjects had the CS+ but not the CS? followed by the UCS. The CS+ and CS? were presented binaurally and separated. The control subjects received no UCS presentations. During the dichotic extinction phase, half of the conditioned subjects had the CS+ presented in the right ear (i.e., with initial left hemisphere input), with the CS? simultaneously presented in the left ear (i.e., with initial right hemisphere input). The other half had the earphones reversed. The control group was similar to the two conditioning groups. During the acquisition phase, significantly larger electrodermal responses were observed to the CS+ compared to the CS? in the conditioning groups, but not in the control group. During the dichotic extinction phase, significantly more resistance to extinction was observed in the CS+ Right-Ear group compared to the CS+ Left-Ear group, with the control group revealing virtually no responding at all. It was concluded that the present results have demonstrated effects of cerebral asymmetry on rate of extinction of the classically conditioned response.     

Left hemisphere advantage for classical conditioning to auditory verbal CSs: Effects of nonattended extinction

The effects of brain laterality, or hemispheric asymmetry, on electrodermal classical conditioning during both attended and nonattended stimulus conditions were studied. Participants were conditioned to consonant-vowel (CV) syllables during an acquisition, or learning, phase of the experiment. During a subsequent extinction phase, the conditioned stimuli (CS) were presented in a dichotic mode of presentation. Half of the participants attended to the left car (right hemisphere) during the extinction phase and the other half of the participants attended to the right ear (left hemisphere). The results showed effects of conditioning for all participants during the acquisition phase. During dichotic extinction, the left hemisphere group showed remaining learning effects in both the attended and nonattended conditions, whereas the right hemisphere group demonstrated conditioning only in the attended condition.     

Differential conditioning to facial emotional expressions: effects of hemispheric asymmetries and CS identification

Previous studies on aversive learning have suggested a right hemispheric advantage for eliciting autonomic reactions to a masked conditioned facial stimulus (CS) depicting anger. The present study investigated the effects of visual field (VF), stimulus awareness, and emotional valence of the CSs on indicators of conditioning (bilateral SCRs, HR) using a differential conditioning paradigm (N = 41). In Group 1, four different negatively valenced facial expressions (CS+) but not four positively valenced CS- were associated with an unconditioned stimulus (US, aversive vocalization, 97 dB, 3 s) during acquisition. Group 2 received a treatment reversal with positive CS+ associated with the US. In a repeated measures design, CSs were presented with or without awareness during extinction (two weeks interval, order counterbalanced). SOAs were adapted for each subject and condition prior to the experiment so that identification performance was approaching chance level. The results revealed that both negative and positive facial expressions could be aversively conditioned providing evidence for a generalization of learning in the valence dimension. During extinction, preattentive negative CS+ presented to the left VF showed a trend towards greater electrodermal and cardiac reactions. However, no such effect emerged under full awareness of the CSs. These results confirm and further specify the nature of hemispheric asymmetries in emotional associative learning.     

Aversive learning in patients with unilateral lesions of the amygdala and hippocampus

The present study applied a visual half field paradigm with emotional facial expressions in patients with selective unilateral amygdalo-hippocampectomy (AHE) to elucidate the contributions of the left and right medial temporal lobe and amygdala to emotional learning. Electrodermal indicators of aversive learning were studied in 14 left AHE and 12 right AHE patients, as well as 13 controls matched in sex and age. In a differential conditioning paradigm with negative (CS+) and positive (CS-) facial expressions, CS+ were associated with an aversive vocalization (US, 95 dB, 3 s). During extinction, stimuli were presented laterally and preattentively using backward masking. Appropriate CS durations yielding preattentive presentation were individually determined prior to conditioning. In contrast to controls, both left and right AHE patients failed to show an autonomic conditioning effect following left visual field presentations of masked negative CS+ during extinction. AHE patients also showed no clear differential acquisition. Moreover, right AHE patients poorly recognised that negative valence was an affiliating dimension of the CS-US compound.     

Orienting and Defensive Reactions to Phobic and Conditioned Fear Stimuli in Phobics and Normals

The aim of this study was to compare cardiovascular and electrodermal responses from subjects conditioned to fear-relevant stimuli with responses from phobics selected to fear the same stimuli. In the first session of the conditioning group slides of either a snake or a spider were presented. One of these served as a CS+ reinforced by an electrical shock and the other as a CS-, which was never followed by shock. In addition the conditioning group was exposed to two neutral pictures (flowers and mushrooms). The phobic group viewed the same type of stimuli and were administered some electrical shocks uncorrelated with the slides. In the second session, randomly formed halves of each group were shown (a) slides of a spider and a snake, or (b) two neutral ones. There were reliable acquisition effects in the conditioning group with the CS+ evoking larger palmar than dorsal skin conductance responses (SCRs) whereas the reverse was true for the CS-. During extinction differential responding to CS+ and CS- was maintained but palmar/dorsal differentiation disappeared. In the phobic group, feared and non-feared cues elicited differential responding with larger palmar SCRs for the feared cue only. The conditioning group failed to evidence heart rate differentiation during acquisition when all heart rate responses (HRRs) were collapsed into a single trial block (TB). When HRRs were grouped into 2 TBs, responses shifted from deceleration to CS+ on TB1 to acceleration on TB2 whereas responses to CS- were unaffected. During extinction, HR exhibited deceleration to both cues but more to CS+ than to CS-. The phobic group's heart rate accelerated to the feared cue and decelerated to the unfeared cues in both sessions. There was no difference between groups' responses to neutral cues during the second session. The results partially validate a conditioning analogue for specific phobias and the inconsistent aspects are discussed in terms of different coping strategies.     

Effects of conditioned stimulus pre-exposure on human electrodermal conditioning to fear-relevant and fear-irrelevant stimuli

The effects of conditioned stimulus (CS) pre-exposure and fear-relevance of the CS on human Pavlovian electrodermal conditioning were investigated. A differential delayed conditioning paradigm was used with a CS-unconditioned stimulus (US; shock) interval of 8 s. In Experiment 1, 64 subjects were randomized into four groups, two of which received fear-relevant stimuli and the other two fear-irrelevant stimuli. Half of the subjects were pre-exposed to the to-be-CSs and the other half to two not-to-be-CSs, with 15 exposure of each stimulus. During acquisition, subjects received 8 reinforced and 8 nonreinforced CS+ and CS- trials, and during the extinction phase 15 nonreinforced trials of each CS. Pre-exposure to the to-be-CSs retarded conditioning for the first and second interval anticipatory responses (FIRs and SIRs); that is, a latent inhibition effect was demonstrated, although the results for the FIR were inconclusive. The expected effects of fear-relevance were not revealed. Experiment 2 addressed the question whether the long pre-exposure period interfered with the frequently observed "preparedness effect" of higher resistance to extinction to fear-relevant stimuli. The design was similar to that of Experiment 1, but for half of the subjects the acquisition phase was initiated immediately after a short rest period, and for the other half acquisition started after an extended rest period, equal to the duration of the pre-exposure phase in Experiment 1. Twenty extinction trials of each CS were presented. A reliable difference in arousal in terms of spontaneous fluctuations was produced by the rest periods, but although differential conditioning was observed, no effect of fear-relevance was seen during extinction.     

Learning to fear suffocation: a new paradigm for interoceptive fear conditioning

The present study aimed to establish a new interoceptive fear conditioning paradigm. The conditioned stimulus (CS) was a flow resistor that slightly obstructs breathing; the unconditional stimulus (US) was a breathing occlusion. The paired group (N = 21) received 6 acquisition trials with paired CS–US presentations. The unpaired group (N = 19) received 6 trials of unpaired CS–US presentations. In the extinction phase, both groups were administered 6 CS‐only trials. Measurements included startle eyeblink response, electrodermal responses, and self‐reported US expectancy. In the paired group, startle blink responses were larger during CS compared to intertrial interval during acquisition and extinction. Electrodermal and US expectancies were larger for the paired than for the unpaired group during acquisition, but not during extinction. The present paradigm successfully established interoceptive fear conditioning with panic‐relevant stimuli.     

Direction of changes in the cardiac component in a Pavlovian conditioning paradigm with variations in CS- and UCS-contents

The research reported was aimed at examining the direction of heart rate post-stimulus changes in a conditioning paradigm with fear-relevant (snakes and spiders), and fear-irrelevant (circles and triangles) slide-CSs. Furthermore, half of the subjects in each group had electric shocks as the UCS, whereas the other two halves were merely threatened about the shock. Finally, all subjects were informed at the start of the extinction about the removal of the UCS. Thus, a 2 X 2 factorial design was used. The conditioning situation involved a differential paradigm with an interstimulus interval of 8 sec. There were 12 presentations of each cue during acquisition, and 20 during extinction. The results showed reliable effects of decelerative acquisition in the fear-relevant shock group, and the fear-irrelevant threat group. During extinction, only the fear-relevant shock group showed evidence of continuing differential responding, with larger deceleration to the CS+. It is speculated that responses to fear-relevant CSs, together with shock-UCSs, share important similarities with the irrational aspect of phobic behavior, since the instructions about the omission of the UCS during extinction did not eliminate the responses to the CS+ in the fear-relevant shock group.     

Effects of Potentially Phobic Conditioned Stimuli on Retention, Reconditioning, and Extinction of the Conditioned Skin Conductance Response

Discriminative classical conditioning of skin conductance responses (SCRs) was studied in 163 college students as a function of four variables: CS type (potentially phobic versus neutral conditioned stimuli), Sex of the subject, Interstimulus interval (ISI) during conditioning (.5 versus 8 s), and Retention interval between conditioning and retention assessment (1 versus 6 months). CS type did not affect acquisition, retention, or reconditioning of the differential conditioned responses. The effect of CS type was highly significant during extinction, with differential SCRs to CS+ and CS- being greater with potentially phobic conditioned stimuli. This was true for both sexes, both the .5-s and the 8-s ISI, and after a 1-month or a 6-month retention interval. Moreover, SCRs conditioned to phobic conditioned stimuli with the .5-s ISI persisted even after subjects' cognitive expectancy of the UCS, which was measured on a trial-by-trial basis, had completely extinguished. The results indicate that the effect of potentially phobic conditioned stimuli on the conditioned skin conductance response is unique to resistance to extinction-they affect not learning but unlearning of the autonomic response.     

Hemispheric priming by meaningful and nonmeaningful symbols in language-trained chimpanzees (Pan troglodytes): further evidence of a left hemisphere advantage.

Hemispheric priming was examined in 3 language-trained chimpanzees (Pan troglodytes) using a simple reaction time paradigm. Subjects were required to hold down a response button until the occurrence of a response cue. A warning stimulus was presented to either the left visual field (LVF) or the right visual field (RVF) before the response cue occurred. No warning stimulus was presented on control trials. The warning stimuli were geometric communicative symbols from two semantic categories: foods and tools. A third set of warning stimuli were familiar geometric symbols. Dependent measures included reaction time and the number of false-positive responses. Reaction-time data indicated an RVF advantage in priming when the warning stimuli were food or tool symbols. No significant visual half-field differences were found for familiar symbols, but a trend toward an RVF advantage was observed. These effects were enhanced when subjects responded with their left hand. False-positive data also indicated an RVF advantage for the food and tool warning stimuli. The data indicate that hemispheric asymmetries for processing communicative symbols are present in language-trained chimpanzees.     

Effects of feedback control on EEG alpha asymmetry during covert mental tasks

EEG alpha (8-12 Hz) was recorded bilaterally from O1-P3 and O2-P4 during two eyes-closed sessions in 40 women. During one session subjects performed two covert right-hemisphere activation tasks and two covert left-hemisphere activation tasks (no-biofeedback condition). During the other session subjects performed the same tasks while trying to control their EEG asymmetries, being provided with EEG asymmetry auditory feedback (biofeedback condition). The ratios of integrated EEG alpha amplitudes were calculated as measure of hemispheric asymmetry, and the number of times that the right and left alpha had the same phase angle was determined as index of hemispheric synchrony (alpha phase index). In both conditions, subjects rated orally after each task their degree of subjective fullfilment of the task. There were significant differences between the EEG asymmetry during right- and left-hemisphere tasks. Significant differences of integrated alpha amplitudes and ratios between the no-biofeedback and biofeedback condition were also found. There was more hemispheric asymmetry in the biofeedback than in the no-biofeedback condition, and a significantly higher alpha phase index. There was no correlation between fullfilment ratings and alpha ratios in the no-biofeedback condition, but there was such correlation during right and left hemisphere tasks in the biofeedback condition. The study demonstrated that biofeedback regulation and covert mental activity can have effects on EEG alpha asymmetry which are cumulative.     

To inhale or not to inhale: conditioned avoidance in breathing behavior in an odor--20% CO2 paradigm

This study investigated breathing behavior in an odor-CO2-inhalation fear conditioning paradigm. A differential conditioning paradigm was applied in 55 participants. Both acquisition and extinction consisted of three CS+ and three CS- trials. Diluted ammonia and butyric acid served as conditional odor cues (CSs); inhalation of 20% CO2-enriched as US. The US was presented 10s after CS+ onset and both stimuli co-terminated 30s later. Subjective anxiety and US-expectancy were measured online upon presentation of the CSs. Respiratory behavior showed a biphasic pattern during CS+ acquisition trials. Participants paradoxically lowered their ventilation first; an increased ventilation was observed only towards the end of the trial. Extinction of this breathing inhibition was found. Participants avoiding the CO2 during acquisition did not show a reduction in fear from acquisition to extinction, whereas Non-avoiders did. We conclude that paradoxical decreases in ventilation constitute a relevant behavioral index of fear in CO2-inhalation paradigms.     

P50 suppression in human discrimination fear conditioning paradigm using danger and safety signals

Auditory P50 suppression, which is assessed using a paired auditory stimuli (S1 and S2) paradigm to record the P50 mid-latency evoked potential, is assumed to reflect sensory gating. Recently, P50 suppression deficits were observed in patients with anxiety disorders, including panic disorder, post-traumatic stress disorder and obsessive-compulsive disorder, as we previously reported. The processes of fear conditioning are thought to play a role in the pathophysiology of anxiety disorders. In addition, we found that the P50 sensory gating mechanism might be physiologically associated with fear conditioning and extinction in a simple human fear-conditioning paradigm that involved a light signal as a conditioned stimulus (CS+). Our objective was to investigate the different patterns of P50 suppression in a discrimination fear-conditioning paradigm with both a CS+ (danger signal) and a CS- (safety signal). Twenty healthy volunteers were recruited. We measured the auditory P50 suppression in the control (baseline) phase, in the fear-acquisition phase, and in the fear-extinction phase using a discrimination fear-conditioning paradigm. Two-way (CSs vs. phase) Analysis of variance with repeated measures demonstrated a significant interaction between the two factors. Post-hoc LSD analysis indicated that the P50 S2/S1 ratio in the CS+ acquisition phase was significantly higher than that in the CS- acquisition phase. These results suggest that the auditory P50 sensory gating might differ according to the cognition of the properties (potentially dangerous or safe) of the perceived signal.     

Does emotion modulate the blink reflex in human conditioning? Startle potentiation during pleasant and unpleasant cues in the picture–picture paradigm

Emotional processes modulate the size of the eyeblink startle reflex in a picture-viewing paradigm, but it is unclear whether emotional processes are responsible for blink modulation in human conditioning. Experiment 1 involved an aversive differential conditioning phase followed by an extinction phase in which acoustic startle probes were presented during CS+, CS-, and intertrial intervals. Valence ratings and affective priming showed the CS+ was unpleasant postacquisition. Blink startle magnitude was larger during CS+ than during CS-. Experiment 2 used the same design in two groups trained with pleasant or unpleasant pictorial USs. Ratings and affective priming indicated that the CS+ had become pleasant or unpleasant in the respective group. Regardless of CS valence, blink startle was larger during CS+ than CS- in both groups. Thus, startle was not modulated by CS valence.     

Callosal involvement in a lateralized stroop task in alcoholic and healthy subjects

To investigate the role of interhemispheric attentional processes, 25 alcoholic and 28 control subjects were tested with a Stroop match-to-sample task and callosal areas were measured with magnetic resonance imaging. Stroop color-word stimuli were presented to the left or right visual field (VF) and were preceded by a color cue that did or did not match the word's color. For matching colors, both groups showed a right VF advantage; for nonmatching colors, controls showed a left VF advantage, whereas alcoholic subjects showed no VF advantage. For nonmatch trials, VF advantage correlated with callosal splenium area in controls but not alcoholic subjects, supporting the position that information presented to the nonpreferred hemisphere is transmitted via the splenium to the hemisphere specialized for efficient processing. The authors speculate that alcoholism-associated callosal thinning disrupts this processing route.     

Human fear conditioning and extinction: Timing is everything…or is it?

A differential fear conditioning paradigm was used with 107 healthy undergraduate participants to evaluate the effect of conditioned stimulus (CS) temporal properties on fear acquisition and extinction. Two minute duration CSs were used for Day 1 fear acquisition. Participants were randomized to receive either 1, 2, or 4 min CS durations during Day 2 extinction. Extinction re-test was examined on Day 3 using the original acquisition CS duration (2 min). Findings indicated that participants who were aware of the CS+/unconditioned stimulus (US) contingency (n = 52) develop a temporal expectation about when the unconditioned stimulus will be delivered. Although the shorter duration CS resulted in greater fear reduction during extinction, cessation of fear responding at re-test was the same for CS extinction durations ranging from half the CS acquisition duration to twice the CS acquisition duration. Thus, extinction performance did not predict extinction at re-test, which could have important implications for optimizing exposure therapy for anxiety disorders.     

The asymmetry of interhemispheric interaction in reverse-stroop task

The purpose of the present study was to examine the effect of interference on interhemispheric interaction in the reverse-stroop task. In two experiments, color-word in black ink and color-patch in red or blue ink were briefly presented to a bilateral visual-field (BVF). The participants were asked to identify the color word, ignoring the color patch. In Experiment 1, color-words written in kanji character were used as target ([Chinese character: see test] or [Chinese character: see test]). In Experiment 2, color-words written in kana character were used as target ([Chinese characters: see test] or [Chinese characters: see test]). The result in Experiment I showed that the size of the interference effect was invariant irrespective of the visual-field of the target. On the contrary, in Experiment 2, the interference effect was larger in the condition where the kana color-word was presented to left visual-field (LVF) than to right visual-field (RVF). These results suggested that the interference effect would be modulated by the dominant hemisphere for processing the target.     

Working memory processes show different degrees of lateralization: evidence from event-related potentials

This study aimed to identify different processes in working memory, using event-related potentials (ERPs) and response times. Abstract polygons were presented for memorization and subsequent recall in a delayed matching-to-sample paradigm. Two polygons were presented bilaterally for memorization and a cue indicated whether one (and if so, which one of the two) or both polygons had to be memorized. A subsequent test figure was presented unilaterally to the left or right visual field and had to be compared with the memorized figure(s). ERP results suggested that memorization takes place in a visual buffer in contralateral posterior brain areas, whereas identification of the test stimulus as a target appears to be mainly a left hemispheric process. Increased response times were found for nontarget test stimuli as compared to targets, and for target test stimuli that were presented contralaterally with respect to the location of the memorized stimulus. In addition, response times were slower when two figures were memorized than when only one was memorized.     

Asymmetrical hemispheric EEG activation evoked by stimulus position during the Simon task

The Simon effect has been previously shown to be asymmetric at both the behavioral and electrophysiological levels. The present investigation was aimed to clarify whether, during a Simon task, hemispheric asymmetry is also observed in the early phases of stimulus processing. In a group of healthy subjects performing the Simon task, we analyzed scalp potentials evoked by the first lateralized cue (left or right), instead of the classical readiness potential preceding the motor response. ERP results showed a significant left cortical activation to stimuli presented in the right visual field at the 140–160 ms time window. Instead, left stimuli elicited a significant activation of the right versus left hemisphere starting at the next 160–180 ms time interval. We linked this asymmetry to that observed in behavioral data: the Simon effect recorded with left stimuli is smaller than the Simon effect recorded with right stimuli. Results confirm the hypothesis that in right handed subjects, left hemisphere is specialized for motor response selection and is able to process right stimuli faster than the right hemisphere does for left stimuli.