The functional organization of auditory working memory as revealed by fMRI.

Spatial and nonspatial auditory tasks preferentially recruit dorsal and ventral brain areas, respectively. However, the extent to which these auditory differences reflect specific aspects of mental processing has not been directly studied. In the present functional magnetic resonance imaging experiment, participants encoded and maintained either the location or the identity of a sound for a delay period of several seconds and then subsequently compared that information with a second sound. Relative to sound localization, sound identification was associated with greater hemodynamic activity in the left rostral superior temporal gyrus. In contrast, localizing sounds recruited greater activity in the parietal cortex, posterior temporal lobe, and superior frontal sulcus. The identification differences were most prominent during the early stage of the trial, whereas the location differences were most evident during the late (i.e., comparison) stage. Accordingly, our results suggest that auditory spatial and identity dissociations as revealed by functional imaging may be dependent to some degree on the type of processing being carried out. In addition, dorsolateral prefrontal and lateral superior parietal areas showed greater activity during the comparison as opposed to the earlier stage of the trial, regardless of the type of auditory task, consistent with results from visual working memory studies.

The functional neuroanatomy of episodic and semantic autobiographical remembering: a prospective functional MRI study.

Autobiographical memory comprises episodic and semantic components mediated by dissociable states of consciousness, one promoting the experience of the self at a specific moment in the past, and the other involving self-knowledge that does not require ''mental time travel.'' These components can be difficult to dissociate using retrospective autobiographical stimuli collection. In this study, we manipulated the episodic/semantic distinction within prospectively collected autobiographical stimuli. Over several months, participants made recordings documenting specific episodes, repeated episodes, and world knowledge. These recordings were later played back to participants during scanning with functional MRI. The results indicated overlapping but distinct patterns of brain activity corresponding to episodic and semantic autobiographical memory. Both episodic and semantic autobiographical memory engaged the left anteromedial prefrontal cortex associated with self-reference, but the episodic condition did so to a greater degree. The episodic condition uniquely engaged the medial temporal, posterior cingulate, and diencephalic regions associated with remote memory recovery. Whereas the episodic condition engaged the right temporo-parietal cortex involved in reconstruction of spatial context and attentional orienting, the semantic condition engaged the left temporo-parietal and parieto-frontal systems involved in egocentric spatial processing and top-down attentional control. Episodic recollection was also associated with suppression of emotional paralimbic regions. These findings support a functional neuroanatomical dissociation between episodic and semantic autobiographical memory, providing concordance to amnesic syndromes with disproportionate impairment in one of these two forms of autobiographical memory.

Distributed self in episodic memory: neural correlates of successful retrieval of self-encoded positive and negative personality traits.

Words processed with reference to the self are generally better remembered than words processed in semantic terms. An account of this phenomenon, labeled the Self Reference Effect (SRE), is that the self promotes elaboration and organization of encoded information. Although a few neuroimaging studies associated self-referential encoding with activations of the medial prefrontal cortex, no previous study has investigated the neural correlates of remembering emotional words encoded in an SRE paradigm. The main goal of this study was to define with fMRI the neural correlates of the successful retrieval of negative and positive personality traits encoded in a self-referential mode. Functional MRI scans were acquired for 11 subjects as they recognized positive and negative emotional personality traits adjectives encoded in a self-referential condition, a semantic condition and in a phonemic condition. The correct recognition of self-encoded personality traits engaged dorso-medial prefrontal cortex and lateral prefrontal regions, premotor cortex, parietal and occipital cortex, caudate and cerebellum. The specific recognition of self-encoded negative personality traits involved greater neural activation in the right extra-striate region than the recognition of positive personality traits. Our fMRI findings suggest that specific processes may operate at both encoding and retrieval to subserve the SRE. Unlike self-encoding, the retrieval of personality traits is modulated by the valence of the stimuli with greater activation for negative words. Our results indicate that personally relevant words may signal important emotional clues and support the notion of a widely distributed set of brain regions involved in maintaining the concepts of self.

Remembering our past: functional neuroanatomy of recollection of recent and very remote personal events.

Functional magnetic resonance imaging was used to study brain regions implicated in retrieval of memories that are decades old. To probe autobiographical memory, family photographs were selected by confederates without the participant's involvement, thereby eliminating many of the variables that potentially confounded previous neuroimaging studies. We found that context-rich memories were associated with activity in lingual and precuneus gyri independently of their age. By contrast, retrosplenial cortex was more active for recent events regardless of memory vividness. Hippocampal activation was related to the richness of re-experiencing (vividness) rather than the age of the memory per se. Remote memories were associated with distributed activation along the rostrocaudal axis of the hippocampus whereas activation associated with recent memories was clustered in the anterior portion. This may explain why circumscribed lesions to the hippocampus disproportionately affect recent memories. These findings are incompatible with theories of long-term memory consolidation, and are more easily accommodated by multiple-trace theory, which posits that detailed memories are always dependent on the hippocampus.

In search of the emotional self: an fMRI study using positive and negative emotional words.

OBJECTIVE: The authors used functional magnetic resonance imaging (fMRI) to define the neural regions mediating self-referential processing of emotional stimuli and to explore how these regions are influenced by the emotional valence of the stimulus. METHOD: Ten healthy subjects were presented with words describing positive and negative personality traits during fMRI scanning in three different conditions. In the self-referential processing condition, subjects judged whether they thought each trait described them. In the other-referential processing condition, subjects judged whether the stimulus described a generally desirable trait. In the letter-recognition control condition, subjects indicated whether the word contained a specific target letter. RESULTS: The self-referential condition induced bilateral activation in the dorsomedial prefrontal cortex, whereas the other-referential condition induced activation in lateral prefrontal areas. Activation in the right dorsomedial prefrontal cortex was unique to the self-referential condition regardless of the valence of the words, although positive words produced a more robust activation than did negative words. In the self-referential condition, differences between the processing of positive and negative words were seen in regions outside the medial frontal cortex, with reductions in the insula, temporal and occipital regions, and inferior parietal regions associated with negative words. CONCLUSIONS: A widely distributed network of brain areas contributes to emotional processing. Among these regions, the right dorsomedial prefrontal cortex is one main area mediating self-reference. By providing a personal perspective in the evaluation of emotional stimuli, the right dorsomedial prefrontal cortex may mediate cognitive processes, such as those involved in psychotherapy, that guide self-regulation of emotional experience.

An fMRI study investigating cognitive modulation of brain regions associated with emotional processing of visual stimuli.

Brain regions modulated by cognitive tasks during emotional processing were investigated using fMRI. Participants performed indirect and direct emotional processing tasks on positive and negative faces and pictures. We used a multivariate technique, partial least squares (PLS) to determine spatially distributed patterns of brain activity associated with different tasks and stimulus conditions, as well as the interaction between the two. The pattern of brain activity accounting for the most task-related covariance represented a task x stimulus interaction and distinguished indirect processing of pictures and direct processing of faces from direct processing of pictures and indirect processing of faces. The latter two conditions were characterised by limbic (e.g. amygdala, insula, thalamus) and temporal lobe activity, in addition to greater activity in the ventral prefrontal cortex. Indirect and direct processing of pictures and faces, respectively, were represented by more dorsal prefrontal and parietal activity. These findings indicate that brain activity during processing of emotional content is critically dependent on both the type of stimulus and processing task. In addition, these results support the idea that the pattern of activity in the emotional network can be influenced in a 'top-down' fashion via cognitive factors such as attentional control, and as such, have important clinical implications for emotional disorders, such as depression and anxiety.