DOI: 10.5061/dryad.qnk98sfkv
title: Cross-modal representation of identity in primate hippocampus

description: Faces and voices are the dominant social signals used to recognize
 individuals amongst human and nonhuman primates. Yet, evidence that
 information across these signals can be integrated into a
 modality-independent representation of individual identity in the primate
 brain has been reported only in human patients. Here we show that, like
 humans, single neurons in the marmoset monkey hippocampus exhibit
 invariant neural responses when presented with the faces or voices of
 specific individuals. However, we also identified a population of single
 neurons in hippocampus that was responsive to the cross-modal identity of
 multiple conspecifics, not only a single individual. An identity network
 model revealed population-level, cross-modal representations of
 individuals in hippocampus, underscoring the broader contributions of many
 neurons to encode identity. This pattern was further evidenced by manifold
 projections of population activity which likewise showed separability of
 individuals, as well as clustering for family members, suggesting that
 multiple learned social categories are encoded as related dimensions of
 identity in hippocampus.  The constellation of findings presented
 here reveals a novel perspective on the neural basis of identity
 representations in primate hippocampus as being both invariant to modality
 and comprising multiple levels of acquired social knowledge.
description: Neurophysiological recordings were performed using 64-channel
 microwire brush arrays while subjects were head and body restrained in a
 chair. Visual stimuli were presented on a LED screen positioned 24 cm in
 front of the animal.  Acoustic stimuli were presented at 70–80 dB SPL. All
 behavior was collected in an anechoic chamber illuminated only by the
 screen. Stimulus presentation was controlled using custom software and eye
 position was monitored by infrared camera tracking of the pupil. Subjects
 initiated trials by holding fixation of gaze for 100ms at a center
 fixation dot on the screen, at which point stimulus presentation was
 initiated. The stimulus consisted of the face and/or voice of a familiar
 conspecific.  Neurophysiological recordings were
 processed into spike times using the open-source package, Spyking Circus
 [1], which were then included in the dataset using custom MATLAB and
 python scripts. Handling of common recording errors is demonstrated in at
 the beginning of the example notebook. Four adult
 marmosets (2 male, 2 female) served as subjects in these experiments. All
 animals are socially housed with 2–8 conspecifics in the Cortical Systems
 and Behavior Laboratory at the University of California San Diego (UCSD).
 All procedures were approved by the Institutional Animal Care and Use
 Committee at the University of California San Diego and follow National
 Institutes of Health guidelines.  [1] Yger P.,
 Spampinato, G.L.B, Esposito E., Lefebvre B., Deny S., Gardella C.,
 Stimberg M., Jetter F., Zeck G. Picaud S., Duebel J., Marre O., A spike
 sorting toolbox for up to thousands of electrodes validated with ground
 truth recordings in vitro and in vivo, eLife 2018;7:e34518
description: No specialized programs and/or software are required to open the
 data.  The data is in a human-readable format that can be opened in most
 text editors.