Electrophysiological classes of layers 2-3 pyramidal cells in monkey

16 The activity of supragranular pyramidal neurons in the dorsolateral prefrontal cortex (DLPFC) 17 neurons is hypothesized to be a key contributor to the cellular basis of working memory in primates. 18 Therefore, the intrinsic membrane properties, a crucial determinant of a neuron's functional properties, are 19 important for the role of DLPFC pyramidal neurons in working memory. The present study aimed to 20 investigate the biophysical properties of pyramidal cells in layers 2-3 of monkey DLPFC in order to create an 21 unbiased electrophysiological classification of these cells. Whole-cell voltage recordings in the slice 22 preparation were performed in 77 pyramidal cells, and 24 electrophysiological measures of their passive and 23 active intrinsic membrane properties were analyzed. Based on the results of cluster analysis of 16 24 independent electrophysiological variables, four distinct electrophysiological classes of monkey pyramidal 25 cells were determined. Two classes contained regular-spiking neurons with low and high excitability and 26 constitute 52% of the pyramidal cells sampled. These subclasses of regular-spiking neurons mostly differ in 27 their input resistance, minimum current that evoked firing and current-to-frequency transduction properties. 28 A third class of pyramidal cells includes low-threshold spiking cells (17%) which fire a burst of 3-5 spikes 29 followed by regular firing at all suprathreshold current intensities. The last class consists of cells with 30 intermediate firing pattern (31%). These cells had two modes of firing response: regular spiking and 31 bursting discharge depending on the strength of stimulation and resting membrane potential. Our results 32 show that diversity in the functional properties of DLPFC pyramidal cells may contribute to 33 heterogeneous modes of information processing during working memory and other cognitive operations 34 that engage the activity of cortical circuits in the superficial layers of the DLPFC. 35