Right hemisphere representation of autonomic conditioning to facial emotional expressions

Angry and fearful compared to happy or neutral faces as conditional stimuli in human fear conditioning: A systematic review and meta-analysis

Some previous research has shown stronger acquisition and impaired extinction of fear conditioned to angry or fearful compared to happy or neutral face conditional stimuli (CS) - a difference attributed to biological 'preparedness'. A systematic review and meta-analysis of fear conditioning studies comparing face CSs of differing expressions identified thirty studies, eighteen of which were eligible for meta-analysis. Skin conductance responses were larger to angry or fearful faces compared to happy or neutral faces during habituation, acquisition and extinction. Significant differences in differential conditioning between angry, fearful, neutral, and happy face CSs were also found, but differences were more prominent between angry and neutral faces compared to angry/fearful and happy faces. This is likely due to lower arousal elicited by neutral compared to happy faces, which may be more salient as CSs. The findings suggest there are small to moderate differences in differential conditioning when angry or fearful compared to happy or neutral faces are used as CSs. These findings have implications for fear conditioning study design and the preparedness theory.

Affect-specific modulation of the N1m to shock-conditioned tones: magnetoencephalographic correlates

Despite its fundamental relevance for representing the emotional world surrounding us, human affective neuroscience research has widely neglected the auditory system, at least in comparison to the visual domain. Here, we have investigated the spatiotemporal dynamics of human affective auditory processing using time-sensitive whole-head magnetoencephalography. A novel and highly challenging affective associative learning procedure, 'MultiCS conditioning', involving multiple conditioned stimuli (CS) per affective category, was adopted to test whether previous findings from intramodal conditioning of multiple click-tones with an equal number of auditory emotional scenes (Bröckelmann et al., 2011 J. Neurosci., 31, 7801) would generalise to crossmodal conditioning of multiple click-tones with an electric shock as single aversive somatosensory unconditioned stimulus (UCS). Event-related magnetic fields were recorded in response to 40 click-tones before and after four contingent pairings of 20 CS with a shock and the other half remaining unpaired. In line with previous findings from intramodal MultiCS conditioning we found an affect-specific modulation of the auditory N1m component 100-150 ms post-stimulus within a distributed frontal-temporal-parietal neural network. Increased activation for shock-associated tones was lateralised to right-hemispheric regions, whereas unpaired safety-signalling tones were preferentially processed in the left hemisphere. Participants did not show explicit awareness of the contingent CS-UCS relationship, yet behavioural conditioning effects were indicated on an indirect measure of stimulus valence. Our findings imply converging evidence for a rapid and highly differentiating affect-specific modulation of the auditory N1m after intramodal as well crossmodal MultiCS conditioning and a correspondence of the modulating impact of emotional attention on early affective processing in vision and audition.

Hemispheric asymmetry: contributions from brain imaging

A series of studies using functional and structural magnetic resonance imaging, including diffusion tensor imaging measures also, to elucidate the aspects of hemispheric asymmetry are reviewed. It is suggested that laterality evolved as a response to the demands of language and the need for air-based communication which may have necessitated a division of labor between the hemispheres in order to avoid having duplicate copies in both the hemispheres that would increase processing redundancy. This would have put pressure on brain structures related to the evolution of language and speech, such as the left peri-Sylvian region. MRI data are provided showing structural and functional asymmetry in this region of the brain and how fibers connecting the right and left peri-Sylvian regions pass through the corpus callosum. It is further suggested that the so-called Yakelovian-torque, i.e., the twisting of the brain along the longitudinal axis, with the right frontal and left occipital poles protruding beyond the corresponding left and right sides, was necessary for the expansion of the left peri-Sylvian region and the right occipito-parietal regions subserving the processing of spatial relations. Functional magnetic resonance imaging data related to sex differences for visuo-spatial processing are presented showing enhanced right-sided activation in posterior parts of the brain in both sexes, and frontal activation including Broca's area in the female group only, suggesting that males and females use different strategies when solving a cognitive task. The paper ends with a discussion of the role of the corpus callosum in laterality and the role played by structural asymmetry in understanding corresponding functional asymmetry. WIREs Cogni Sci 2011 2 461-478 DOI: 10.1002/wcs.122 For further resources related to this article, please visit the WIREs website.

"Hearing voices": auditory hallucinations as failure of top-down control of bottom-up perceptual processes

Auditory hallucination is a key characteristic of schizophrenia that seriously debilitates the patient, with consequences for social engagement with others. Hallucinatory experiences are also observed in healthy individuals in the general population who report "hearing voices" in the absence of an external acoustic input. A view on auditory hallucinations and "hearing voices" is presented that regards such phenomena as perceptual processes, originating from speech perception areas in the left temporal lobe. Healthy individuals "hearing voices" are, however, often aware that the experience comes from inner thought processes, which is not reported by hallucinating patients. A perceptual model can therefore, not alone explain the difference in the phenomenology of how the "voices heard" are attributed to either an inner or outer cause. An expanded model is thus presented which takes into account top-down cognitive control, localized to prefrontal cortical areas, to inhibit and re-attribute the perceptual mis-representations. The expanded model is suggested to be empirically validated using a dichotic listening speech perception paradigm with instructions for top-down control of attention focus to either the right or left side in auditory space. It is furthermore suggested to use fMRI to validate the temporal and frontal lobe neuronal correlates of the cognitive processes involved in auditory hallucinations.

Recognizing emotion from facial expressions: psychological and neurological mechanisms

Recognizing emotion from facial expressions draws on diverse psychological processes implemented in a large array of neural structures. Studies using evoked potentials, lesions, and functional imaging have begun to elucidate some of the mechanisms. Early perceptual processing of faces draws on cortices in occipital and temporal lobes that construct detailed representations from the configuration of facial features. Subsequent recognition requires a set of structures, including amygdala and orbitofrontal cortex, that links perceptual representations of the face to the generation of knowledge about the emotion signaled, a complex set of mechanisms using multiple strategies. Although recent studies have provided a wealth of detail regarding these mechanisms in the adult human brain, investigations are also being extended to nonhuman primates, to infants, and to patients with psychiatric disorders.

Les visages et leurs émotions

Faces represent a crucial vector of interhuman communication. The message transmitted by the face has multiple features. Recognition of each feature can be impaired independently or in combination with others. In order to understand the behavioral consequences of such impairments, which can be a major social handicap, we first must specify the neural networks involved in face recognition. We propose in this first part to present the systems involved in face recognition, in particular the question of identity and prosopagnosia. Different neural networks are indeed implicated in the recognition of invariant facial features such as identity, gender, ethnicity, and recognition of variant features like facial expression and eye gaze. This paper is illustrated by some of our scalp and intracranial electrophysiological studies performed in humans allowing us to describe some aspects of face recognition dynamics combining an excellent spatial and temporal resolution. Intracranial recordings were performed in drug refractory epileptical patients implanted with depth electrodes. These studies demonstrate that numerous deep brain and cortical structures participate early and sometimes in a sustained manner in face recognition.

Imaging emotional brain functions: conceptual and methodological issues

This article reviews the psychophysiological and brain imaging literature on emotional brain function from a methodological point of view. The difficulties in defining, operationalising and measuring emotional activation and, in particular, aversive learning will be considered. Emotion is a response of the organism during an episode of major significance and involves physiological activation, motivational, perceptual, evaluative and learning processes, motor expression, action tendencies and monitoring/subjective feelings. Despite the advances in assessing the physiological correlates of emotional perception and learning processes, a critical appraisal shows that functional neuroimaging approaches encounter methodological difficulties regarding measurement precision (e.g., response scaling and reproducibility) and validity (e.g., response specificity, generalisation to other paradigms, subjects or settings). Since emotional processes are not only the result of localised but also of widely distributed activation, a more representative model of assessment is needed that systematically relates the hierarchy of high- and low-level emotion constructs with the corresponding patterns of activity and functional connectivity of the brain.

Functional neuroimaging of emotional learning and autonomic reactions

This article provides a selective overview of the functional neuroimaging literature with an emphasis on emotional activation processes. Emotions are fast and flexible response systems that provide basic tendencies for adaptive action. From the range of involved component functions, we first discuss selected automatic mechanisms that control basic adaptational changes. Second, we illustrate how neuroimaging work has contributed to the mapping of the network components associated with basic emotion families (fear, anger, disgust, happiness), and secondary dimensional concepts that organise the meaning space for subjective experience and verbal labels (emotional valence, activity/intensity, approach/withdrawal, etc.). Third, results and methodological difficulties are discussed in view of own neuroimaging experiments that investigated the component functions involved in emotional learning. The amygdala, prefrontal cortex, and striatum form a network of reciprocal connections that show topographically distinct patterns of activity as a correlate of up and down regulation processes during an emotional episode. Emotional modulations of other brain systems have attracted recent research interests. Emotional neuroimaging calls for more representative designs that highlight the modulatory influences of regulation strategies and socio-cultural factors responsible for inhibitory control and extinction. We conclude by emphasising the relevance of the temporal process dynamics of emotional activations that may provide improved prediction of individual differences in emotionality.

Analysis of Evoked EEG Synchronization and Desynchronization During Perception of Emotiogenic Stimuli: Association with Autonomic Activation Processes

The cortical apparatus involved in performing autonomic responses in conditions of emotional activation has received little study. The aim of the present work was to assess the dynamics of evoked EEG synchronization and desynchronization at different frequency ranges during the perception of emotiogenic visual stimuli depending on the extent of accompanying autonomic activation as measured by skin galvanic responses. Studies were performed on 33 students (all right-handed) aged 18-28 years. Difference between subjects with weak (SGR(-)) and strong (SGR(+)) skin galvanic responses were seen only in the theta1 range (4-6 Hz). At the stage at which emotiogenic information was perceived (the first second after the start of stimulus presentation), both groups showed similar dynamics of increases in evoked synchronization in the parietal-temporal-occipital areas of the cortex, with greater involvement of the right hemisphere. From the second second to the end of presentation (2-6 sec), emotiogenic signals gave significantly greater levels of evoked synchronization in these cortical areas as compared with neutral stimuli, and only in the SGR(+) group. These data provide evidence for the involvement of the posterior areas of the cortex of the right hemisphere in the mechanisms of motivational attention and sympathetic activation.

Strength of visual percept generated by famous faces perceived without awareness: Effects of affective valence, response latency, and visual field

Participants who were unable to detect familiarity from masked 17 ms faces (Stone and Valentine, 2004 and Stone and Valentine, in press-b) did report a vague, partial visual percept. Two experiments investigated the relative strength of the visual percept generated by famous and unfamiliar faces, using masked 17 ms exposure. Each trial presented simultaneously a famous and an unfamiliar face, one face in LVF and the other in RVF. In one task, participants responded according to which of the faces generated the stronger visual percept, and in the other task, they attempted an explicit familiarity decision. The relative strength of the visual percept of the famous face compared to the unfamiliar face was moderated by response latency and participants' attitude towards the famous person. There was also an interaction of visual field with response latency, suggesting that the right hemisphere can generate a visual percept differentiating famous from unfamiliar faces more rapidly than the left hemisphere. Participants were at chance in the explicit familiarity decision, confirming the absence of awareness of facial familiarity.

Accuracy of familiarity decisions to famous faces perceived without awareness depends on attitude to the target person and on response latency

Stone and Valentine (2004) presented masked 17 ms faces in simultaneous pairs of one famous and one unfamiliar face. Accuracy in selecting the famous face was higher when the famous person was regarded as "good" or liked than when regarded as "evil" or disliked. Experiment 1 attempted to replicate this phenomenon, but produced a different pattern of results. Experiment 2 investigated alternative explanations and found evidence supporting only the effect of response latency: responses made soon after stimulus onset were more accurate to liked than to disliked faces, whereas responses made after a longer delay were equally accurate to disliked faces. It appears that the effect of negative valence was corrected within the space of a few hundred milliseconds. Experiment 3, using an affective priming paradigm, supported the concept that an early-arising effect of valence is corrected if it is misleading to the directed task.

Neural basis of fear conditioning induced by video clip: positron emission tomography study

In patients with post-traumatic stress disorder (PTSD), re-experiencing the trauma is often induced by external cues in the environment. The cues, which were emotionally neutral for the patients before the traumatic event, become fearful ones after the event. This phenomenon is considered to be associated with fear conditioning. The paradigm was set up so that the emotionality changes in the patients with PTSD would be reproduced, and the regional cerebral blood flow (rCBF) measured with positron emission tomography (PET) was compared during exposure to the same stimuli before and after acquisition of fear conditioning. Ten healthy male subjects were asked to look at some emotionally neutral photos, then to watch a video with fearful content that also contained images similar to that presented in the photos, and afterwards to look at the photos again. Five of the 10 subjects felt that the object in the photos was more fearful after watching the video than before, and they were considered to have acquired fear conditioning. In those five subjects, the rCBF in the right amygdala and the left posterior cingulate gyrus after acquisition of fear conditioning significantly increased relative to the rCBF before conditioning. Thus, these regions seem to have a critical role in fear conditioning.

Processing of a simple aversive conditioned stimulus in a divided visual field paradigm: an fMRI study

A left visual hemifield advantage for the processing of negative facial expressions has been demonstrated in a variety of studies. We tested whether the same effect is found for a neutral facial expression that had acquired a negative meaning through pairing with an aversive event. Startle reflex amplitudes, skin-conductance responses (SCR), and two verbal measures of affect (negative valence and arousal) were significantly increased after pairing, but no stimulation side by pairing interaction was observed. Functional magnetic resonance imaging (fMRI) revealed a significant increase of BOLD (blood oxygen level dependent) activity in the medial prefrontal cortex (MPFC), and the right frontal opercular region (RFOP). MPFC activity was correlated with psychophysiological and verbal emotional responses across subjects and, like these responses, was independent of the stimulation side. In contrast, RFOP activity was significantly stronger during left than during right hemifield stimulation but did not correlate with psychophysiological or verbal measures of negative affect. These results suggest that emotional responses to an aversive conditioned expressively neutral face are similar in both visual hemifields. MPFC activity seems to be closely linked to the strength of these responses.

Better the devil you know? Nonconscious processing of identity and affect of famous faces

The nonconscious recognition of facial identity was investigated in two experiments featuring brief (17-msec) masked stimulus presentation to prevent conscious recognition. Faces were presented in simultaneous pairs of one famous face and one unfamiliar face, and participants attempted to select the famous face. Subsequently, participants rated the famous persons as "good" or "evil" (Experiment 1) or liked or disliked (Experiment 2). In Experiments 1 and 2, responses were less accurate to faces of persons rated evil/disliked than to faces of persons rated good/liked, and faces of persons rated evil/disliked were selected significantly below chance. Experiment 2 showed the effect in a within-items analysis: A famous face was selected less often by participants who disliked the person than by participants who liked the person, and the former were selected below chance accuracy. The within-items analysis rules out possible confounding factors based on variations in physical characteristics of the stimulus faces and confirms that the effects are due to participants' attitudes toward the famous persons. The results suggest that facial identity is recognized preconsciously, and that responses may be based on affect rather than familiarity.

Dissociating prelexical and postlexical processing of affective information in the two hemispheres: effects of the stimulus presentation format

Using a lexical decision task, the authors investigated whether brain asymmetries in the detection of emotionally negative semantic associations arise only at a perceptually discriminative stage at which lexical analysis is accurate or can already be found at crude and incomplete levels of perceptual representation at which word-nonword discrimination is based solely on guessing. Emotionally negative and neutral items were presented near perceptual threshold in the left and right visual hemifields. Word-nonword discrimination performance as well as the bias to classify a stimulus as a "word" (whether or not it actually is a word) were assessed for a normal, horizontal stimulus presentation format (Experiment 1) and for an unusual, vertical presentation format (Experiment 2). Results show that while the two hemispheres are equally able to detect affective semantic associations at a prelexical processing stage (both experiments), the right hemisphere is superior at a postlexical, perceptually discriminative stage (Experiment 2). Moreover, the findings suggest that only an unusual, nonoverlearned stimulus presentation format allows adequate assessment of the right hemisphere's lexical-semantic skills.

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.

Fears, phobias, and preparedness: toward an evolved module of fear and fear learning

An evolved module for fear elicitation and fear learning with 4 characteristics is proposed. (a) The fear module is preferentially activated in aversive contexts by stimuli that are fear relevant in an evolutionary perspective. (b) Its activation to such stimuli is automatic. (c) It is relatively impenetrable to cognitive control. (d) It originates in a dedicated neural circuitry, centered on the amygdala. Evidence supporting these propositions is reviewed from conditioning studies, both in humans and in monkeys; illusory correlation studies; studies using unreportable stimuli; and studies from animal neuroscience. The fear module is assumed to mediate an emotional level of fear learning that is relatively independent and dissociable from cognitive learning of stimulus relationships.

Contextual and auditory fear conditioning are mediated by the lateral, basal, and central amygdaloid nuclei in rats

A large body of literature implicates the amygdala in Pavlovian fear conditioning. In this study, we examined the contribution of individual amygdaloid nuclei to contextual and auditory fear conditioning in rats. Prior to fear conditioning, rats received a large electrolytic lesion of the amygdala in one hemisphere, and a nucleus-specific neurotoxic lesion in the contralateral hemisphere. Neurotoxic lesions targeted either the lateral nucleus (LA), basolateral and basomedial nuclei (basal nuclei), or central nucleus (CE) of the amygdala. LA and CE lesions attenuated freezing to both contextual and auditory conditional stimuli (CSs). Lesions of the basal nuclei produced deficits in contextual and auditory fear conditioning only when the damage extended into the anterior divisions of the basal nuclei; damage limited to the posterior divisions of the basal nuclei did not significantly impair conditioning to either auditory or contextual CS. These effects were typically not lateralized, although neurotoxic lesions of the posterior divisions of the basal nuclei had greater effects on contextual fear conditioning when the contralateral electrolytic lesion was placed in the right hemisphere. These results indicate that there is significant overlap within the amygdala in the neural pathways mediating fear conditioning to contextual and acoustic CS, and that these forms of learning are not anatomically dissociable at the level of amygdaloid nuclei.

Neural responses to salient visual stimuli

The neural mechanisms involved in the selective processing of salient or behaviourally important stimuli are uncertain. We used an aversive conditioning paradigm in human volunteer subjects to manipulate the salience of visual stimuli (emotionally expressive faces) presented during positron emission tomography (PET) neuroimaging. Increases in salience, and conflicts between the innate and acquired value of the stimuli, produced augmented activation of the pulvinar nucleus of the right thalamus. Furthermore, this pulvinar activity correlated positively with responses in structures hypothesized to mediate value in the brain right amygdala and basal forebrain (including the cholinergic nucleus basalis of Meynert). The results provide evidence that the pulvinar nucleus of the thalamus plays a crucial modulatory role in selective visual processing, and that changes in perceptual salience are mediated by value-dependent plasticity in pulvinar responses.

Cortical systems for the recognition of emotion in facial expressions

This study is part of an effort to map neural systems involved in the processing of emotion, and it focuses on the possible cortical components of the process of recognizing facial expressions. We hypothesized that the cortical systems most responsible for the recognition of emotional facial expressions would draw on discrete regions of right higher-order sensory cortices and that the recognition of specific emotions would depend on partially distinct system subsets of such cortical regions. We tested these hypotheses using lesion analysis in 37 subjects with focal brain damage. Subjects were asked to recognize facial expressions of six basic emotions: happiness, surprise, fear, anger, disgust, and sadness. Data were analyzed with a novel technique, based on three-dimensional reconstruction of brain images, in which anatomical description of surface lesions and task performance scores were jointly mapped onto a standard brain-space. We found that all subjects recognized happy expressions normally but that some subjects were impaired in recognizing negative emotions, especially fear and sadness. The cortical surface regions that best correlated with impaired recognition of emotion were in the right inferior parietal cortex and in the right mesial anterior infracalcarine cortex. We did not find impairments in recognizing any emotion in subjects with lesions restricted to the left hemisphere. These data provide evidence for a neural system important to processing facial expressions of some emotions, involving discrete visual and somatosensory cortical sectors in right hemisphere.

Cognitive influences on human autonomic nervous system function

Recent studies of human autonomic nervous system function have challenged the traditional view that the parasympathetic and sympathetic branches have opposite effects. In addition, studies of autonomic activity that accompanies attention, orienting and learning have demonstrated that the autonomic nervous system is not simply a 'non-cognitive' and automatic part of brain function. The autonomic and central nervous systems are intimately related, and new research is beginning to link brain function with autonomic function in a dynamic way.

The role of the right hemisphere in the physiological and cognitive components of emotional processing

Right hemisphere specialization for emotional processing was investigated using behavioral and psychophysiological methods. Fifty undergraduates were shown slides depicting negative emotional and neutral scenes briefly lateralized to the right or left cerebral hemispheres and asked to categorize each as emotional or neutral. Pulse volume and heart rate (HR) measured physiological processing and reaction time measured cognitive processing. The largest vasoconstriction responses and HR deceleration were obtained for emotional items in the right hemisphere. However, reaction time failed to show right hemisphere superiority in perceptual/cognitive processing, demonstrating instead slowest responses to emotional stimuli presented to the right hemisphere together with evidence for left hemisphere competence. Selective right hemispheric activation in autonomic responses, combined with the lack of right hemisphere specialization in the cognitive task, suggests that the physiological response system rather than the perceptual/cognitive system is the locus of the right hemisphere superiority for emotion.

Lateralized startle probes in the study of emotion

Two experiments are reported in which affective modulation of the startle reflex elicited by monaurally presented acoustic probes was further examined. An earlier study in our laboratory obtained significant modulation by affect for probes presented to the left ear, but no significant effect for probes presented to the right ear. Experiment 1 replicated the procedures used in that experiment and obtained the same pattern of effects. Experiment 2 changed the presentation of monaural probes from a blocked to a mixed presentation and again obtained a similar pattern. Modulatory differences in reflex magnitude between pleasant and unpleasant stimuli were consistently large and reliable for reflexes elicited by left ear probes but weak and unreliable for reflexes elicited by right ear probes.

Central representation of chronic ongoing neuropathic pain studied by positron emission tomography

This study was undertaken to explore whether the neural substrates demonstrated in brain imaging studies on experimentally induced pain are involved in the perception of chronic neuropathic pain. We investigated the cerebral representation of chronic lateralised ongoing pain in patients with painful mononeuropathy (PMN, i.e., pain in the distribution of a nerve, neuralgia) with positron emission tomography (PET), using regional cerebral blood flow (rCBF) as an index for neuronal activity. Eight patients (29-53 years) with PMN in the lower extremity (4 in the right, 4 in the left) were recruited. Paired comparisons of rCBF were made between the patient's habitual pain (HP) state and the pain alleviated (PA) state following a successful regional nerve block (RNB) with lidocaine. The ongoing neuropathic pain resulted in activation of bilateral anterior insula, posterior parietal, lateral inferior prefrontal, and posterior cingulate cortices as well as the posterior sector of the right anterior cingulate cortex (ACC), Brodmann area (BA) 24, regardless of the side of PMN. In addition, a reduction in rCBF was noted in the contralateral posterior thalamus. No significant change of rCBF was detected in the somatosensory areas, i.e., SI and SII. The cerebral activation pattern, while addressing the differences between the HP and PA states, emphasises the affective-motivational dimension in chronic ongoing neuropathic pain. The striking preferential activation of the right ACC (BA 24), regardless of the side of the PMN, not only confirms that the ACC participates in the sensorial/affectional aspect of the pain experience but also suggests a possible right hemispheric lateralisation of the ACC for affective processing in chronic ongoing neuropathic pain. Our data suggests that the brain employs different central mechanisms for chronic neuropathic pain and experimentally induced acute pain, respectively.

Brain asymmetry and autonomic conditioning: sensitization control

In the present experiment we report effects of cerebral asymmetry, or laterality, during classical conditioning to facial emotional stimuli. Twenty-five female subjects were presented with slides of a happy face in one visual half-field (VHF), and simultaneously a slide of an angry face in the other VHF, followed by shock as the unconditioned stimulus (UCS). To control for effects of sensitization, a new stimulus, never associated with the UCS, was introduced in the extinction phase. Dependent measures were phasic heart rate responses (HR) and skin conductance responses (SCR). The HR results showed a significant right hemisphere effect for the CS-UCS association, that was not attributable to UCS sensitization. No significant effects were found for the SCRs. The basic HR finding was a right hemisphere superiority for learning of a conditioned association.

Cerebral asymmetry in autonomic conditioning to facial expressions: sex differences

In the present experiment, sex differences in hemispheric asymmetry during classical conditioning to emotional stimuli are reported. 125 subjects (62 females and 63 males) were shown a slide of a happy face in the right (or left) visual half field (VHF), and simultaneously a slide of an angry face in the left (or right) VHF. Eight groups were formed by the combination of male and female subjects; left and right VHF positions of the angry/happy faces; and the administration/omission of the shock unconditioned stimulus (UCS). Dependent measures were skin conductance responses recorded from both hands. The results during extinction showed a significant larger SCR magnitude to the shock compared to the no-shock groups only for the female subjects. CS position during conditioning was also important in revealing differential responding to either the happy or angry faces. A right hemisphere effect was found for the angry face CS for both the male and female subjects, however with a greater difference for the females.