Self-face recognition activates a frontoparietal “mirror” network in the right hemisphere: an event-related fMRI study

Functional and Neural Mechanisms of Embodiment: Importance of the Vestibular System and the Temporal Parietal Junction

Embodiment, the sense of being localized within one's physical body, is a fundamental aspect of the self. Recent research shows that self and body processing as well as embodiment require distinct brain mechanisms. Here, we review recent clinical and neuroimaging research on multisensory perception and integration as well as mental imagery, pointing out their importance for the coding of embodiment at the temporo-parietal junction (TPJ). Special reference is given to vestibular mechanisms that are relevant for self and embodiment and to methods that interfere experimentally with normal embodiment. We conclude that multisensory and vestibular coding at the TPJ mediates humans' experience as being embodied and spatially situated, and argue that pathologies concerning the disembodied self, such as out-of-body experience or other autoscopic phenomena, are due to deficient multisensory integration at the TPJ.

Cytology and functionally correlated circuits of human posterior cingulate areas

Human posterior cingulate cortex (PCC) and retrosplenial cortex (RSC) form the posterior cingulate gyrus, however, monkey connection and human imaging studies suggest that PCC area 23 is not uniform and atlases mislocate RSC. We histologically assessed these regions in 6 postmortem cases, plotted a flat map, and characterized differences in dorsal (d) and ventral (v) area 23. Subsequently, functional connectivity of histologically guided regions of interest (ROI) were assessed in 163 [(18)F]fluorodeoxyglucose human cases with PET. Compared to area d23, area v23 had a higher density and larger pyramids in layers II, IIIc, and Vb and more intermediate neurofilament-expressing neurons in layer Va. Coregisrtration of each case to standard coordinates showed that the ventral branch of the splenial sulci coincided with the border between d/v PCC at -5.4 +/- 0.17 cm from the vertical plane and +1.97 +/- 0.08 cm from the bi-commissural line. Correlation analysis of glucose metabolism using histologically guided ROIs suggested important circuit differences including dorsal and ventral visual stream inputs, interactions between the vPCC and subgenual cingulate cortex, and preferential relations between dPCC and the cingulate motor region. The RSC, in contrast, had restricted correlated activity with pericallosal cortex and thalamus. Visual information may be processed with an orbitofrontal link for synthesis of signals to drive premotor activity through dPCC. Review of the literature in terms of a PCC duality suggests that interactions of dPCC, including area 23d, orient the body in space via the cingulate motor areas, while vPCC interacts with subgenual cortex to process self-relevant emotional and non-emotional information and objects and self-reflection.

Split-brain reveals separate but equal self-recognition in the two cerebral hemispheres

To assess the ability of the disconnected cerebral hemispheres to recognize images of the self, a split-brain patient (an individual who underwent complete cerebral commissurotomy to relieve intractable epilepsy) was tested using morphed self-face images presented to one visual hemifield (projecting to one hemisphere) at a time while making "self/other" judgments. The performance of the right and left hemispheres of this patient as assessed by a signal detection method was not significantly different, though a measure of bias did reveal hemispheric differences. The right and left hemispheres of this patient independently and equally possessed the ability to self-recognize, but only the right hemisphere could successfully recognize familiar others. This supports a modular concept of self-recognition and other-recognition, separately present in each cerebral hemisphere.

Right-hemisphere motor facilitation by self-descriptive personality-trait words

The emergent picture from the literature on the processing of self-related information suggests that in addition to the neural mechanisms involved in recognizing one's own face, there may also be neural representations of the self that are modality independent and favour the right hemisphere. We used focal, single-pulse transcranial magnetic stimulation in human subjects to assess cortical excitability during covert reading of self-descriptive personality-trait words. We hypothesized that the right hemisphere would show a greater overall facilitation to personality-trait words than the left hemisphere. Overall, personality-trait words led to significantly greater motor facilitation in the right hemisphere than in the left hemisphere. In addition, words rated as 'never' self-characteristic yielded significant right hemisphere facilitation, and words rated as 'always' self-characteristic showed a similar trend. The results are discussed in terms of the notion that the right hemisphere plays a dominant role in both self-relevant processing and the processing of affective stimuli.