Area PEc Neurons Use a Multiphasic Pattern of Activity to Signal the Spatial Properties of Optic Flow.

Milena Raffi,Roberta Calzavara,Salvatore Squatrito,Alessandro Piras

doi:10.1155/2017/6495872

Abstract

The cortical representation of visual perception requires the integration of several-signal processing distributed across many cortical areas, but the neural substrates of such perception are largely unknown. The type of firing pattern exhibited by single neurons is an important indicator of dynamic circuitry within or across cortical areas. Neurons in area PEc are involved in the spatial mapping of the visual field; thus, we sought to analyze the firing pattern of activity of PEc optic flow neurons to shed some light on the cortical processing of visual signals. We quantified the firing activity of 152 optic flow neurons using a spline interpolation function, which allowed determining onset, end, and latency of each neuronal response. We found that many PEc neurons showed multiphasic activity, which is strictly related to the position of the eye and to the position of the focus of expansion (FOE) of the flow field. PEc neurons showed a multiphasic activity comprised of excitatory phases interspersed with inhibitory pauses. This phasic pattern seems to be a very efficient way to signal the spatial location of visual stimuli, given that the same neuron sends different firing patterns according to a specific combination of FOE/eye position.

Highlights

Area PEc is a multimodal area of the posterior parietal cortex involved in several functional processes, including optic flow processing [1,2,3,4], reaching arm movements [5, 6], and eye position encoding [7]
The phase determination analysis has been carried out in each visual neuron for each focus of expansion (FOE) and/or eye position for every condition resulting in a data set composed of 4060 different stimulations (44 conditions did not have a sufficient number of trials, so they were not considered for the analysis)
Battaglia-Mayer and coworkers [36] showed that the activity of most PEc cells is related to the direction of movement and to the hand position, both being influenced by eye position. This phasic pattern seems to be a very efficient way to signal the spatial location of visual stimuli given that the same neuron is able to send different firing patterns, that is, different inputs to target areas, according to the FOE/eye position

Summary

Introduction

Area PEc is a multimodal area of the posterior parietal cortex involved in several functional processes, including optic flow processing [1,2,3,4], reaching arm movements [5, 6], and eye position encoding [7]. Maimon and Assad [21] found that during the execution of arm movements, neurons in the parietal area 5 show a rampinglike activity as well as a burst/pause neural activity. These reaching-related neurons ramped up or down their firing rate prior to the beginning of movement, and such gradual changes in firing were not related to occurring differences in the visual input presentation

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