Social cognition, including complex social judgments and attitudes, is shaped by individual learning experiences, where affect often plays a critical role. Aversive classical conditioning-a form of associative learning involving a relationship between a neutral event (conditioned stimulus, CS) and an aversive event (unconditioned stimulus, US)-represents a well-controlled paradigm to study how the acquisition of socially relevant knowledge influences behavior and the brain. Unraveling the temporal unfolding of brain mechanisms involved appears critical for an initial understanding about how social cognition operates. Here, 128-channel ERPs were recorded in 50 subjects during the acquisition phase of a differential aversive classical conditioning paradigm. The CS+ (two fearful faces) were paired 50% of the time with an aversive noise (CS upward arrow + /Paired), whereas in the remaining 50% they were not (CS upward arrow + /Unpaired); the CS- (two different fearful faces) were never paired with the noise. Scalp ERP analyses revealed differences between CS upward arrow + /Unpaired and CS- as early as approximately 120 ms post-stimulus. Tomographic source localization analyses revealed early activation modulated by the CS+ in the ventral visual pathway (e.g. fusiform gyrus, approximately 120 ms), right middle frontal gyrus (approximately 176 ms), and precuneus (approximately 240 ms). At approximately 120 ms, the CS- elicited increased activation in the left insula and left middle frontal gyrus. These findings not only confirm a critical role of prefrontal, insular, and precuneus regions in aversive conditioning, but they also suggest that biologically and socially salient information modulates activation at early stages of the information processing flow, and thus furnish initial insight about how affect and social judgments operate.
We used fMRI to examine amygdala activation in response to fearful facial expressions, measured over multiple scanning sessions. 15 human subjects underwent three scanning sessions, at 0, 2 and 8 weeks. During each session, functional brain images centered about the amygdala were acquired continuously while participants were shown alternating blocks of fearful, neutral and happy facial expressions. Intraclass correlation coefficients calculated across the sessions indicated stability of response in left amygdala to fearful faces (as a change from baseline), but considerably less left amygdala stability in responses to neutral expressions and for fear versus neutral contrasts. The results demonstrate that the measurement of fMRI BOLD responses in amygdala to fearful facial expressions might be usefully employed as an index of amygdala reactivity over extended periods. While signal change to fearful facial expressions appears robust, the experimental design employed here has yielded variable responsivity within baseline or comparison conditions. Future studies might manipulate the experimental design to either amplify or attenuate this variability, according to the goals of the research.
Recent evidence suggests that frontal brain electrical activity reveals asymmetries in activation in response to positive vs negative affective stimuli. This study was designed to evaluate whether this asymmetry is present at birth. Newborn infants were presented with water followed by a sucrose solution and then by a citric acid solution. Facial expression was videotaped during the presentation of the liquids and EEG was recorded from the frontal and parietal scalp regions on the left and right side. Usable EEG data were obtained from 16 newborn infants in response to these taste conditions. Videotaping of facial expression in response to these stimuli indicated the presence of disgust during both water (the first taste introduced) and citric acid. EEG was Fourier Transformed and power in the 1-3, 3-6 and 6-12 Hz bands was computed. The findings revealed that the water condition produced reductions in right-hemisphere power in the two higher frequency bands in both the scalp regions compared with the other two conditions. The sucrose condition produced greater relative left-sided activation in both regions compared with the water condition. These data, in conjunction with our previous findings of asymmetries in 10-month-old infants, indicate that stimulus-elicited affective asymmetries in brain electrical activity are present at birth.
BACKGROUND: EEG alpha power has been demonstrated to be inversely related to mental activity and has subsequently been used as an indirect measure of brain activation. The hypothesis that the thalamus serves as a neuronal oscillator of alpha rhythms has been supported by studies in animals, but only minimally by studies in humans. METHODS: In the current study, PET-derived measures of regional glucose metabolism, EEG, and structural MRI were obtained from each participant to assess the relation between thalamic metabolic activity and alpha power in depressed patients and healthy controls. The thalamus was identified and drawn on each subject's MRI. The MRI was then co-registered to the corresponding PET scan and metabolic activity from the thalamus extracted. Thalamic activity was then correlated with a 30-min aggregated average of alpha EEG power. RESULTS: Robust inverse correlations were observed in the control data, indicating that greater thalamic metabolism is correlated with decreased alpha power. No relation was found in the depressed patient data. CONCLUSIONS: The results are discussed in the context of a possible abnormality in thalamocortical circuitry associated with depression.
Spatial working memory is a cognitive brain mechanism that enables the temporary maintenance and manipulation of spatial information. Recent neuroimaging and behavioral studies have led to the proposal that directed spatial attention is the mechanism by which location information is maintained in spatial working memory. Yet it is unclear whether attentional involvement is required throughout the period of active maintenance or is only invoked during discrete task-phases such as mnemonic encoding. In the current study, we aimed to track the time-course of attentional involvement during spatial working memory by recording event-related brain potentials (ERPs) from healthy volunteers. In Experiment 1, subjects performed a delayed-recognition task. Each trial began with the presentation of a brief stimulus (S1) that indicated the relevant location that subjects were to maintain in working memory. A 4.8-5.3 sec delay interval followed during which a single task-irrelevant probe was presented. The delay interval concluded with a test item (S2) to which subjects made a response indicating whether the S2-location was the same as the S1-memory location. To determine if attention was differentially engaged during discrete phases of the trial, task-irrelevant probes were presented early (400-800 msec following S1-offset) or late (2600-3000 msec following S1-offset) during the delay interval. Sensory-evoked ERPs (P1 and N1) elicited by these irrelevant probes showed attention-like modulations with greater amplitude responses for probes occurring at the S1-memory locations in comparison to probes presented at other locations. This pattern was obtained for both early- and late-delay probes. Probe-evoked activity during delayed-recognition trials was similar to activity observed when spatial attention was explicitly focused on a location in visual space (Experiment 2). These results are consistent with a model of spatial working memory in which perceptual level selective attention is utilized throughout the entire period of active maintenance to keep relevant spatial information in mind.
Planned and reflexive behaviors often occur in the presence of emotional stimuli and within the context of an individual's acute emotional state. Therefore, determining the manner in which emotion and attention interact is an important step toward understanding how we function in the real world. Participants in the current investigation viewed centrally displayed, task-irrelevant, face distractors (angry, neutral, happy) while performing a lateralized go/no-go continuous performance task. Lateralized go targets and no-go lures that did not spatially overlap with the faces were employed to differentially probe processing in the left (LH) and right (RH) cerebral hemispheres. There was a significant interaction between expression and hemisphere, with an overall pattern such that angry distractors were associated with relatively more RH inhibitory errors than neutral or happy distractors and happy distractors with relatively more LH inhibitory errors than angry or neutral distractors. Simple effects analyses confirmed that angry faces differentially interfered with RH relative to LH inhibition and with inhibition in the RH relative to happy faces. A significant three-way interaction further revealed that state anxiety moderated relations between emotional expression and hemisphere. Under conditions of low cognitive load, more intense anxiety was associated with relatively greater RH than LH impairment in the presence of both happy and threatening distractors. By contrast, under high load, only angry distractors produced greater RH than LH interference as a function of anxiety.
Recent neuroimaging and neuropsychological work has begun to shed light on how the brain responds to the viewing of facial expressions of emotion. However, one important category of facial expression that has not been studied on this level is the facial expression of pain. We investigated the neural response to pain expressions by performing functional magnetic resonance imaging (fMRI) as subjects viewed short video sequences showing faces expressing either moderate pain or, for comparison, no pain. In alternate blocks, the same subjects received both painful and non-painful thermal stimulation. Facial expressions of pain were found to engage cortical areas also engaged by the first-hand experience of pain, including anterior cingulate cortex and insula. The reported findings corroborate other work in which the neural response to witnessed pain has been examined from other perspectives. In addition, they lend support to the idea that common neural substrates are involved in representing one's own and others' affective states.
Four experiments testing right-handed adult males examined interhemispheric transfer time (IHTT) estimation with visual evoked potentials (EPs) elicited in response to hemiretinal presentations of checkerboard-flash stimuli. Experiment 1 was a study of the relation between reaction time (RT) and EP measures of IHTT. EP measures provided more valid estimates than RT measures because more subjects showed IHTT in the direction of anatomical prediction. Experiment 2 showed that EPs derived from lateral occipital sites provided more valid and longer estimates of IHTT compared with EPs from medial occipital sites. Experiment 3 showed no difference between random versus blocked hemiretinal stimuli. Experiment 4 showed that IHTT derived with a linked-ears reference provided more valid estimates than IHTT derived with a mid-frontal reference and that small changes in stimulus eccentricity did not influence IHTT. The findings of these experiments indicate that noninvasive estimates of visual IHTT can be obtained in humans.
This commentary provides reflections on the current state of affairs in research on EEG frontal asymmetries associated with affect. Although considerable progress has occurred since the first report on this topic 25 years ago, research on frontal EEG asymmetries associated with affect has largely evolved in the absence of any serious connection with neuroscience research on the structure and function of the primate prefrontal cortex (PFC). Such integration is important as this work progresses since the neuroscience literature can help to understand what the prefrontal cortex is "doing" in affective processing. Data from the neuroscience literature on the heterogeneity of different sectors of the PFC are introduced and more specific hypotheses are offered about what different sectors of the PFC might be doing in affect. A number of methodological issues associated with EEG measures of functional prefrontal asymmetries are also considered.