Task-related dissociation of EEG ß enhancement and suppression.

Previous investigations of EEG ß processes can be divided into two categories: one in which ß enhancement is obtained and one in which ß suppression is obtained. The current study investigated the ß band range (14-30Hz) by subdividing the signal into 2Hz sub-bands. We presented participants with photographs of faces expressing happy, angry, sad or neutral expressions under two primary tasks in which participants judged the emotion the individual was expressing, or how the way the other person feels makes the participant feel. Results revealed a pattern of both ß suppression and enhancement that appeared to depend on whether the task required first-person emotional experience (self-task) or perspective-taking (other-task). Specifically, the self-task was associated with enhancement while the other-task was associated with suppression. While some previous research has reported ß enhancement to emotion-inducing stimuli, other research has reported ß suppression in tasks also associated with mu suppression. To our knowledge, the current data are the first to reveal both ß enhancement and suppression within a single experiment and suggests a neurocognitive dissociation of enhancement and suppression within the ß band range.

Attentional distraction, µ-suppression and empathic perspective-taking.

Social mirroring has been proposed to be an automatic process whereby an observer understands the intentions of others by using his/her motor system to simulate others' actions. Automaticity implies that if the observer's eyes are fixed on another person, the observer's mirror system will engage whether attention is focused on the other person or not. This proposal has not been fully tested, however. The current study therefore addressed whether µ-suppression, an electroencephalographic measure of putative mirror neuron activity, induced by observing the actions of others would be affected by attentional distraction. Participants performed two different distraction tasks while watching a video of a hand repeatedly touching the forefinger and thumb together. µ-suppression was compared across three different blocks: (1) video with no distraction, (2) video with mental imagery distraction and (3) video with word generation distraction. While the no distraction condition yielded the typical level of µ-suppression, the word generation distraction task eliminated any evidence of µ-suppression suggesting that simply fixating the eyes on an action without focusing attention is insufficient to induce µ-suppression. A secondary goal of the current experiment was to replicate correlational findings between µ-suppression and empathic perspective-taking. A counterintuitive, negative relationship between µ-suppression and perspective-taking was replicated, and a theoretical model for explaining this relationship is offered.

Differences in self- and other-induced Mu suppression are correlated with empathic abilities.

Recent research suggests a role of the human mirror neuron system in empathic processing. Electroencephalographic (EEG) mu suppression in the 8-13Hz band-range has been proposed to reflect mirror-like activation of sensorimotor cortices. We therefore investigated the relationship between suppression in the 8-13Hz range and empathic abilities as measured by the Interpersonal Reactivity Index (IRI). Based on previous work showing significant differences between execution- and observation-related mu suppression and on theories of empathy pointing to the importance of discriminating self from other, we predicted that the size of this difference within individuals would correlate with participants' perspective-taking abilities. Larger differences in execution- and observation-induced mu suppression were associated with greater scores on the perspective-taking subscale of the IRI. The current data are therefore consistent with the claim that neural activity reflected in mu suppression is related to empathic abilities.

Brain regions and their dynamics in prospective memory retrieval: a MEG study.

We measured brain activity using magnetoencephalography in five participants during ongoing tasks that included prospective memory, retrospective memory, and oddball trials. Sources were identified in the hippocampal formation and posterior parietal and frontal lobes. Posterior parietal cortex activation had an earlier onset in the prospective memory condition than retrospective memory or oddball conditions, a higher level of theta activity in the retrospective condition, and higher levels of upper alpha in the prospective and oddball conditions. Activation of the hippocampal formation had a longer duration in the retrospective memory and prospective memory conditions than the oddball condition, but prominent alpha and theta band activity was present in all three conditions. We interpret the early (87 ms) onset of activity in parietal cortex as evidence for an initial noticing of appropriate conditions for a PM response. Hippocampal activity may reflect a subsequent memory search for the intended action.

Neural correlates of differential retrieval orientation: Sustained and item-related components.

Retrieval orientation refers to a cognitive state that biases processing of retrieval cues in service of a specific goal. The present study used a mixed fMRI design to investigate whether adoption of different retrieval orientations - as indexed by differences in the activity elicited by retrieval cues corresponding to unstudied items - is associated with differences in the state-related activity sustained across a block of test trials sharing a common retrieval goal. Subjects studied mixed lists comprising visually presented words and pictures. They then undertook a series of short test blocks in which all test items were visually presented words. The blocks varied according to whether the test items were used to cue retrieval of studied words or studied pictures. In several regions, neural activity elicited by correctly classified new items differed according to whether words or pictures were the targeted material. The loci of these effects suggest that one factor driving differential cue processing is modulation of the degree of overlap between cue and targeted memory representations. In addition to these item-related effects, neural activity sustained throughout the test blocks also differed according to the nature of the targeted material. These findings indicate that the adoption of different retrieval orientations is associated with distinct neural states. The loci of these sustained effects were distinct from those where new item activity varied, suggesting that the effects may play a role in biasing retrieval cue processing in favor of the current retrieval goal.

Electrophysiological dissociation of the neural correlates of recollection and familiarity.

Event-related potentials (ERPs) were employed to investigate electrophysiological correlates of recognition memory in a task that allowed segregation of test items according to whether they were recollected (operationalized by introspective report) or, if recollection failed, their level of familiarity (operationalized by recognition confidence). The amplitude of a negative-going ERP deflection that onsets around 300 ms post-stimulus varied inversely with familiarity strength. This effect was maximal over the left frontal scalp. It did not differ between the ERPs elicited by highly familiar versus recollected items, indicating that the recollection is not merely a consequence of strong familiarity. By contrast, a later positive deflection (onset ca. 500 ms post-stimulus) was enhanced in ERPs elicited by recollected relative to highly familiar items. This effect was maximal over the left posterior scalp and was insensitive to familiarity, as indicated by its absence in the contrast between items judged highly familiar versus highly unfamiliar. The findings constitute a double dissociation between the neural correlates of recollection and familiarity. Together with the results of a parallel functional magnetic resonance imaging study (A.P. Yonelinas et al., J. Neurosci. (2005), 25, 3002-3008), they indicate that recollection and familiarity rely on qualitatively distinct neural systems and strongly support dual-process models of recognition memory.

MEG reveals different contributions of somatomotor cortex and cerebellum to simple reaction time after temporally structured cues.

Magnetoencephalography (MEG) was used to measure brain activity while participants performed a simple reaction to targets after either a random interval (uncued targets) or a series of isochronous warning stimuli with 200-ms intervals that acted as a countdown. Targets could arrive "on time" or "early" relative to the preceding warning stimuli. Cerebellar activity before any stimulus onset predicted uncued simple reaction time. Onset of activity in somatomotor cortex relative to the target predicted reaction time after two warning stimuli when the target arrived on time or early. After three warning stimuli, when the target arrived on time and was certain to occur, prestimulus cerebellar activity and somatomotor onset were significant predictors of reaction time. When the target arrived early after three warning stimuli, prestimulus cerebellar and cingulate activity were predictive. The cerebellar results may reflect a number of possible factors, including a role in timing, response readiness, prediction and attention.

Age-related effects on superior temporal gyrus activity during an auditory oddball task.

We used magnetoencephalography in combination with magnetic resonance imaging to investigate the effects of aging on the temporal dynamics of activity localized to several brain regions during an auditory oddball task. The most interesting effects were noted in the superior temporal gyrus as follows: (1) responses were generally stronger to rare than to frequent tones throughout the entire 600-ms time interval, and (2) increases in the amplitude of the 40-ms peak and the latency of the maximum late response were evident in the elderly. Although superior temporal gyrus activity has traditionally been associated with early sensory processing, these results suggest that superior temporal gyrus activity is also important for later decision-related processing.

Content-specificity of the neural correlates of recollection.

It is widely assumed that episodic retrieval (recollection) involves reinstatement of cortical activity engaged during the processing of an episode when it was initially experienced. It follows from this assumption that the cortical correlates of recollection should differ with the content of what is recollected, and that retrieval of different content should be associated with activity in functionally distinct cortical regions. The present experiment investigated these predictions. Subjects (N=17) studied a mixed list of words and pictures and were then presented with a test list comprised of words only. Test items were studied words, the names of studied pictures, and unstudied (new) words. Functional magnetic resonance images were acquired while the subjects made Remember/Know/New judgments to these test words. Independent of study material, studied items endorsed as Remembered elicited greater activity than correctly classified unstudied items in several regions, including left frontal, left lateral parietal, and posterior cingulate cortex. In addition, Remembered items elicited greater activity in the right hippocampus and parahippocampal gyrus than items accorded Know judgments, replicating previous findings. Analysis of content-specific effects demonstrated a regional double-dissociation within left fusiform cortex; recollected words elicited greater activity than recollected pictures in lateral fusiform, whereas the reverse effect was evident in an anterior fusiform region. The lateral and anterior fusiform areas correspond closely to areas held to be functionally specialized for the processing of visual words and pictures, respectively. Thus, the current findings support the cortical reinstatement hypothesis of episodic retrieval.