Julio Martinez¹ (), Michael Feyerabend¹, Stefan Pommer², Andreas Neef², Jochen Staiger², Wataru Inoue¹; ¹Schulich School of Medicine and Dentistry, Western University, London, Ontario, ²Institute for Neuroanatomy, University Medical Center Göttingen, Georg-August University, Göttingen, Germany

Primates have specialized visual pathways composed of interconnected cortical areas. The input area V1 contains neurons that encode basic visual features, whereas downstream in the lateral prefrontal cortex (LPFC), neurons can acquire tuning for novel complex feature associations. It has been tacitly assumed that each visual cortical area is composed of repeatable neuronal subtypes (i.e., cell types follow the principle of serial homology), and that variations in synaptic strength and connectivity patterns underlie an area’s functional specialization. Here, we test the hypothesis that diversity in the intrinsic makeup of single neurons contributes to area specialization along the visual pathways. We recorded intracellularly from 463 neurons in slices obtained from 42 marmosets (Callithrix jacchus). Of these, 363 neurons passed a quality control pipeline: 107 V1 and 256 LPFC cells (BA 8/46). A total of 144 neurons were examined histologically and classified as aspiny/inhibitory (29%) or spiny/excitatory (71%). Additionally, 32 cells were reconstructed. We measured morphological and electrophysiological features of single neurons and trained a random forest classifier using these features to separate neurons into three main subtypes: excitatory neurons, fast-spiking interneurons, and non-fast-spiking interneurons. We focus on fast-spiking inhibitory interneurons and excitatory cells because the classifier reliably identified these categories. Excitatory neurons in the LPFC were larger, less excitable, and fired broader spikes than V1 neurons. Some inhibitory fast-spiking interneurons in the LPFC had longer axons and fired spikes with longer latencies and a more depolarized action potential trough than those in V1. Intrinsic bursting was found in subpopulations of both excitatory and inhibitory LPFC neurons, but not in V1 neurons. The latter may favor temporal summation of spikes and, therefore, enhanced synaptic plasticity in the LPFC relative to V1. Our results show that specialization within the primate visual system permeates the most basic processing level: the single neuron.