Visual Information Routes in the Posterior Dorsal and Ventral Face Network Studied with Intracranial Neurophysiology and White Matter Tract Endpoints.

Occipitotemporal regions within the face network process perceptual and socioemotional information, but the dynamics and information flow between different nodes of this network are still debated. Here, we analyzed intracerebral EEG from 11 epileptic patients viewing a stimulus sequence beginning with a neutral face with direct gaze. The gaze could avert or remain direct, while the emotion changed to fearful or happy. N200 field potential peak latencies indicated that face processing begins in inferior occipital cortex and proceeds anteroventrally to fusiform and inferior temporal cortices, in parallel. The superior temporal sulcus responded preferentially to gaze changes with augmented field potential amplitudes for averted versus direct gaze, and large effect sizes relative to other network regions. An overlap analysis of posterior white matter tractography endpoints (from 1066 healthy brains) relative to active intracerebral electrodes in the 11 patients showed likely involvement of both dorsal and ventral posterior white matter pathways. Overall, our data provide new insight into the timing of face and social cue processing in the occipitotemporal brain and anchor the superior temporal cortex in dynamic gaze processing.

Representation of the bird's own song in the canary HVC: contribution of broadly tuned neurons.

In songbirds, neurons in the song nucleus HVC exhibit a striking example of selective auditory response, firing more to playback of the bird's own song (BOS) than to conspecific songs. This song selectivity has been found in various songbird species, both those that sing a single individual-specific song as well as those, such as the canary, in which both song structure and individual-identity encoding in song is more complex. In the present study, we investigated how the BOS is represented in the HVC of anesthetized long-day canaries by using temporal and spectral variants of the BOS stimulus. We addressed the question of how selective HVC neurons were by quantifying the number of song elements, called phrases, that evoked auditory responses. Phrases that were individual-specific or that were frequently delivered in an individual's songs did not drive HVC neurons to a greater degree than others. Reordering phrases or altering their acoustic structure caused a decrease in the auditory responsiveness of HVC neurons. This sensitivity to the spectral and temporal features of the BOS involved neurons that failed to respond to BOS variants or were driven by a reduced number of phrases, as well as neurons whose auditory responsiveness extended beyond the features of the individual's song, responding to phrases that were not sung by the bird itself. Therefore, the neural strategy by which BOS structure is represented in the canary HVC may require something other than a strict representation of the repertoire of song components. We suggest that the individual's song could be coded, at least in part, by an ensemble of broadly tuned neurons.