Functional Clusters of Neurons in Layer 6 of Macaque V1

Abstract

Layer 6 appears to perform a very important role in the function of macaque primary visual cortex, V1, but not enough is understood about the functional characteristics of neurons in the layer 6 population. It is unclear to what extent the population is homogeneous with respect to their visual properties or if one can identify distinct subpopulations. Here we performed a cluster analysis based on measurements of the responses of single neurons in layer 6 of primary visual cortex in male macaque monkeys (Macaca fascicularis) to achromatic grating stimuli that varied in orientation, direction of motion, spatial and temporal frequency, and contrast. The visual stimuli were presented in a stimulus window that was also varied in size. Using the responses to parametric variation in these stimulus variables, we extracted a number of tuning response measures and used them in the cluster analysis. Six main clusters emerged along with some smaller clusters. Additionally, we asked whether parameter distributions from each of the clusters were statistically different. There were clear separations of parameters between some of the clusters, particularly for f1/f0 ratio, direction selectivity, and temporal frequency bandwidth, but other dimensions also showed differences between clusters. Our data suggest that in layer 6 there are multiple parallel circuits that provide information about different aspects of the visual stimulus.

Multiple gamma rhythms carry distinct spatial frequency information in primary visual cortex

“…We further assumed that the GCs would change with the SF of the visual stimulus. Accordingly, the amplitudes of the 3 oscillatory components were modeled as the difference of Gaussian functions [ 45 – 48 ], and their peak frequencies were modeled using the Naka–Rushton function [ 49 – 52 ] (see Materials and methods for the descriptive model and model fitting).…”

Contrast response in a comprehensive network model of macaque V1

“…(The L6 firing rates are known to be quite high, with a synaptic failure rate of about 50%.) Between these two extreme values of R, we assume f( R ) is increasing and has the shape of a sigmoidal function which is quite reasonable based on L6 firing rates ( Hawken et al., 2019 ).…”

A Closer Look at Corticothalamic “Loops”

“…Third, in macaque primary visual cortex, six main functional clusters have been reported based on responsiveness to visual stimuli (i.e., achromatic gratings, with varying parameters; Hawken et al, 2020 ). Transcriptomic identity was not determined, nor the actual connectional identity of the neurons (i.e., whether these project to the LGN, or the claustrum, or are solely intrinsic); but these data might be expected from continuing work, as in other reports in mouse (e.g., Tasic et al, 2018 ; Cembrowski and Spruston, 2019 ).…”