Successful interpersonal interactions rely on an ability to read the emotional states of others and to modulate one's own behavior in response. The actions of others serve as valuable social stimuli in this respect, offering the observer an insight into the actor's emotional state. Social cognition continues to mature throughout adolescence. Here we assess longitudinally the development of functional connectivity during early adolescence within two neural networks implicated in social cognition: one network of brain regions consistently engaged during action observation and another one associated with mentalizing. Using fMRI, we reveal a greater recruitment of the social–emotional network during the observation of angry hand actions in male relative to female adolescents. These findings are discussed in terms of known sex differences in adolescent social behavior.

Repetitive TMS (rTMS) provides a noninvasive tool for modulating neural activity in the human brain. In healthy participants, rTMS applied over the language-related areas in the left hemisphere, including the left posterior temporal area of Wernicke (LTMP) and inferior frontal area of Broca, have been shown to affect performance on word recognition tasks. To investigate the neural substrate of these behavioral effects, off-line rTMS was combined with fMRI acquired during the performance of a word recognition task. Twenty right-handed healthy men underwent fMRI scans before and after a session of 10-Hz rTMS applied outside the magnetic resonance scanner. Functional magnetic resonance images were acquired during the performance of a word recognition task that used English or foreign-language words. rTMS was applied over the LTMP in one group of 10 participants (LTMP group), whereas the homologue region in the right hemisphere was stimulated in another group of 10 participants (RTMP group). Changes in task-related fMRI response (English minus foreign languages) and task performances (response time and accuracy) were measured in both groups and compared between pre-rTMS and post-rTMS. Our results showed that rTMS increased task-related fMRI response in the homologue areas contralateral to the stimulated sites. We also found an effect of rTMS on response time for the LTMP group only. These findings provide insights into changes in neural activity in cortical regions connected to the stimulated site and are consistent with a hypothesis raised in a previous review about the role of the homologue areas in the contralateral hemisphere for preserving behavior after neural interference.

The objective of this study was to investigate potential sex differences in the neural response to human bodies using fMRI carried out in healthy young adults. We presented human bodies in a block-design experiment to identify body-responsive regions of the brain, namely, extrastriate body area (EBA) and fusiform body area (FBA). In a separate event-related “adaptation” experiment, carried out in the same group of subjects, we presented sets of four human bodies of varying body size and shape. Varying levels of body morphing were introduced to assess the degree of morphing required for adaptation release. Analysis of BOLD signal in the block-design experiment revealed significant Sex × Hemisphere interactions in the EBA and the FBA responses to human bodies. Only women showed greater BOLD response to bodies in the right hemisphere compared with the left hemisphere for both EBA and FBA. The BOLD response in right EBA was higher in women compared with men. In the adaptation experiment, greater right versus left hemisphere response for EBA and FBA was also identified among women but not men. These findings are particularly novel in that they address potential sex differences in the lateralization of EBA and FBA responses to human body images. Although previous studies have found some degree of right hemisphere dominance in body perception, our results suggest that such a functional lateralization may differ between men and women.

Studies in both human and nonhuman primates indicate that motor and premotor cortical regions participate in auditory and visual perception of actions. Previous studies, using transcranial magnetic stimulation (TMS), showed that perceiving visual and auditory speech increased the excitability of the orofacial motor system during speech perception. Such studies, however, cannot tell us which brain regions mediate this effect. In this study, we used the technique of combining positron emission tomography with TMS to identify the brain regions that modulate the excitability of the motor system during speech perception. Our results show that during auditory speech perception, there is increased excitability of motor system underlying speech production and that this increase is significantly correlated with activity in the posterior part of the left inferior frontal gyrus (Broca's area). We propose that this area “primes” the motor system in response to heard speech even when no speech output is required and, as such, operates at the interface of perception and action.

Successful recovery of words from episodic memory relies strongly on semantic processes at the time of encoding. Evidence from several functional magnetic resonance imaging (fMRI) studies has shown that changes in neural activity in the left inferior prefrontal cortex (LIPFC) during semantic encoding predict subsequent memory performance. This evidence has been taken to suggest that LIPFC plays a critical role in memory formation. Functional neuroimaging findings, however, do not establish a causal brain-behavior relationship. To determine whether there is a causal link between LIPFC involvement at encoding and subsequent success in memory performance, we conducted a two-part study in which we first used fMRI to localize encoding-related activation in LIPFC and then employed repetitive transcranial magnetic stimulation (rTMS) to manipulate neural processes in LIPFC during semantic encoding. To demonstrate the neuroanatomical specificity of any observed effect and to control for nonspecific rTMS side effects, we also stimulated neural processes in two control sites. Using frameless stereotaxy, we positioned the stimulation coil to target (1) the LIPF region that was activated during fMRI (mean xyz = −48 35 5); (2) the homologous righthemisphere region; and (3) an additional left parietal control site. At each site, “stimulated” items (600 msec of 7-Hz rTMS with Cadwell Round Coil) were intermixed with items presented without concurrent stimulation. Subsequently, subjects performed a recognition memory task for the words encountered. We found support for the predicted causal brain-behavior relationship, which was specific to LIPFC. When comparing recognition scores for stimulated items, normalized for variations in performance on nonstimulated trials, we found that words encoded under LIPFC stimulation were subsequently recognized with higher accuracy than words encoded under stimulation in the two cortical control sites. By contrast, no performance difference emerged when the two control sites were compared with each other. Based on additional analyses of the rTMS effects observed directly at the time of encoding (i.e., on semantic-decision performance), we suggest that LIPFC stimulation may have produced its effect on recognition memory, at least in part, through the triggering of more extensive processing of the stimulated items and an ensuing gain in item distinctiveness. Physiological processes of facilitation probably also contributed to the observed memory benefit. Together, these findings suggest that LIPFC does play a causal role in episodic memory formation.

When looking at one object, human subjects can shift their attention to another object in their visual field without moving the eyes. Such shifts of attention activate the same brain regions as those involved in the execution of eye movements. Here we investigate the role of one of the main cortical oculomotor area, namely, the frontal eye field (FEF), in shifts of attention. We used transcranial magnetic stimulation (TMS), a technique known to disrupt transiently eye-movements preparation. We hypothesized that if the FEF is a necessary element in the network involved in shifting attention without moving the eyes, then TMS should also disrupt visuospatial attention. For each volunteer, we positioned the TMS coil over the probabilistic anatomical location of the FEF, and we verified that single pulses delayed eye movements. We then applied TMS during a visuospatial attention task. In this task, a central arrow directed shifts of attention and the subject responded by a keypress to a subsequent visual peripheral target without moving the eyes from the central fixation point. In a few trials, the cue was invalid or uninformative, yielding slower responses than when the cue was valid. We delivered single pulses either 53 msec before or 70 msec after target onset. Contrary to our prediction, the main effect of the stimulation was a decrease in reaction time when it was applied 53 msec before target onset. TMS over the left hemisphere facilitated responses to targets in the right hemifield only and for all cueing conditions, whereas TMS over the right hemisphere had a bilateral effect for valid and neutral but not invalid cueing. Thus, TMS interfered with shift of attention only in the case of right hemisphere stimulation: it increased the cost of invalid cueing. Our results suggest that TMS over the FEF facilitates visual detection, and thereby reduces reaction time. This finding provides new insights into the role of the human FEF in processing visual information. The functional asymmetry observed for both facilitation of visual detection and interference with shifts of attention provides further evidence for the dominance of the right hemisphere for those processes. Our results also underline that the disruptive or facilitative effect of TMS over a given region depends upon the behavioral context.

The neural mechanisms underlying hypnotic states and responses to hypnotic suggestions remain largely unknown and, to date, have been studied only with indirect methods. Here, the effects of hypnosis and suggestions to alter pain perception were investigated in hypnotizable subjects by using positron emission tomography (PET) measures of regional cerebral blood flow (rCBF) and electroencephalographic (EEG) measures of brain electrical activity. The experimental conditions included a restful state (Baseline) followed by hypnotic relaxation alone (Hypnosis) and by hypnotic relaxation with suggestions for altered pain unpleasantness (Hypnosis-with-Suggestion). During each scan, the left hand was immersed in neutral (35°C) or painfully hot (47°C) water in the first two conditions and in painfully hot water in the last condition. Hypnosis was accompanied by significant increases in both occipital rCBF and delta EEG activity, which were highly correlated with each other ( r = 0.70, p < 0.0001). Peak increases in rCBF were also observed in the caudal part of the right anterior cingulate sulcus and bilaterally in the inferior frontal gyri. Hypnosis-related decreases in rCBF were found in the right inferior parietal lobule, the left precuneus, and the posterior cingulate gyrus. Hypnosis-with-suggestions produced additional widespread increases in rCBF in the frontal cortices predominantly on the left side. Moreover, the medial and lateral posterior parietal cortices showed suggestion-related increases overlapping partly with regions of hypnosis-related decreases. Results support a state theory of hypnosis in which occipital increases in rCBF and delta activity reflect the alteration of consciousness associated with decreased arousal and possible facilitation of visual imagery. Frontal increases in rCBF associated with suggestions for altered perception might reflect the verbal mediation of the suggestions, working memory, and top-down processes involved in the reinterpretation of the perceptual experience. These results provide a new description of the neurobiological basis of hypnosis, demonstrating specific patterns of cerebral activation associated with the hypnotic state and with the processing of hypnotic suggestions.

Vigilance behavior, or watch keeping, involves the focusing of attention on the detection of subtle changes in the environment that occur over a long period of time. We investigated the time course of changes in brain activity during the continuous performance of a 60-min auditory vigilance task. The task required the detection of an intensity drop that occurred in 5% of the auditory stimuli. Six 1-min samples of cerebral blood flow (CBF) and electroencephalographic (EEG) activity were obtained at l0-min intervals during the vigilance performance. Changes in CBF were measured by means of positron emission tomography (PET). Performance data (hits, false alarms, reaction time) were analyzed across six 10-min blocks. Eight healthy male volunteers participated in the study. During the 60-min test, the number of correct detections (hits) did not change, but both the reaction time and EEG activity in the theta (4 to 7 Hz) range progressively increased across testing. CBF in several subcortical structures (thalamus, substantia innominata, and putamen) and cortical areas (ventrolateral, dorsolateral, and orbital frontal cortex; parietal cortex; and temporal cortex) decreased as a function of time-on-task; changes in the cortical regions were limited to the right hemisphere. Blood flow also decreased in the temporalis muscles. At the same time, CBF increased in several visual cortical areas including the left and right fusiform gyri. Furthermore, the thalamic blood-flow response co-varied with that in the substantia innominata, the ponto-mesencephalic tegmentum, and the anterior cingulate cortex. The right ventrolateral-frontal blood-flow response covaried with that in the right parietal, orbitofrontal, and dorsolateral frontal cortex. 'Iko main conclusions are drawn from the obtained data. First, we suggest that the observed time-related changes in reaction time, EEG activity, and blood flow in the temporalis muscles are related to changes in the level of arousal (alertness) and that CBF changes in the thalamus-related neural circuitry represent a brain correlate of such changes. Second, we speculate that time-related CBF decreases in cortical regions of the right hemisphere underlie a shift from controlled to automatic attentional processing of the auditory stimuli.