Functional connectivity within the visual cortex of the rat shows state changes

Abstract

The aim of this study was to investigate the dynamics of the horizontal functional connectivity within the visual cortex during spontaneous activity or during visual stimulation. Two arrays of 16 electrodes were inserted in the visual cortex of a rat. From these electrodes a depth profile was obtained of the local spiking activity. The cross-correlations between all electrodes were estimated. Three types of cross-correlation peaks were identified and classified as; 'thin peaks', 'fast waves' and 'slow waves'. Partialization was applied, a mathematical method to reduce the amount of common input in correlations, and its effect on the three types of correlation peaks was studied. Slow waves were found to be the most vulnerable to partialization and thin peaks the least. From these observations it was concluded that the three types of peaks represent synchronous neuronal assemblies of different magnitude; slow waves large, fast waves intermediate and thin peaks assemblies composed of small numbers of neurons. Large changes were observed in the types of cross-correlations and their spatial distribution within the set of interarray combinations of electrodes. These changes were spontaneous, and could not be related to the visual stimulation. Two states were identified; the 'thin-peak' state and the 'slow-wave' state. The 'thin-peak' state is interpreted as occurring at a light level of anaesthesia and is characterized by the presence of thin peaks in all combinations of electrodes. Thin peaks with the largest strength were found in the upper interarray electrode combinations. The 'slow-wave' state is interpreted as occurring at a deep level of anaesthesia and is characterized by the presence of exclusively slow waves, which were limited mostly to the middle and lower interarray combinations of electrodes. Activation of the cortex is thus associated with the appearance of synchrony between small groups of neurons (thin peaks) which, in contrast to the slow-wave state, include the upper layers of the cortex.

Changes in Functional Connectivity within the Rat Striatopallidal Axis during Global Brain Activation In Vivo

“…This reduction in low-frequency ECoG activity was accompanied by a significant increase (25 Ϯ 13%; p ϭ 0.03, two way paired t test) in the power of activities between 55 and 80 Hz. These data are consistent with the sensory stimulus eliciting cortical activation and, indeed, more global activation (Munk et al, 1996;Steriade et al, 1996;van der Togt et al, 1998;Destexhe et al, 1999).…”

Neuronal synchrony does not represent texture segregation

“…Synchrony of ®ring between all possible combinations of two electrodes with RFs suf®ciently separate to allow for all three conditions`in±in' ,`in±out', and out±out' (n 172) was assessed by computing the normalized cross-correlation coef®cients 29 . Cross-correlations were calculated over the full 600-ms time window following stimulus onset, during which time the monkeys maintained ®xation, and after which they responded with a correct eye movement to the ®gure position.…”

“…Average rate was subtracted from the responses before calculation. To remove stimulus-locked components from the cross-correlations, we used the technique of linear partialization of the cross-correlations 29 .…”

The relation of ongoing brain activity, evoked neural responses, and cognition

“…It therefore appears sensible to compare results from such studies with those where context has been explicitly modulated by introducing cues that prepare for an upcoming cognitive challenge. Several studies have employed such cues to study the variability of evoked neural and perceptual responses to a single stimulus (or a group of equivalent stimuli) (Super et al, 2003; Sapir et al, 2005; Thut et al, 2006; Wyart and Tallon-Baudry, 2009). Typically, in these paradigms, a cue will appear that can indicate a task-relevant location or feature for a stimulus that will be presented after a brief but often variable delay.…”