Directed coupling in local field potentials of macaque V4 during visual short-term memory revealed by multivariate autoregressive models

Abstract

Processing and storage of sensory information is based on the interaction between different neural populations rather than the isolated activity of single neurons. In order to characterize the dynamic interaction and transient cooperation of sub-circuits within a neural network, multivariate autoregressive (MVAR) models have proven to be an important analysis tool. In this study, we apply directed functional coupling based on MVAR models and describe the temporal and spatial changes of functional coupling between simultaneously recorded local field potentials in extrastriate area V4 during visual memory. Specifically, we compare the strength and directional relations of coupling based on generalized partial directed coherence (GPDC) measures while two rhesus monkeys perform a visual short-term memory task. In both monkeys we find increases in theta power during the memory period that are accompanied by changes in directed coupling. These interactions are most prominent in the low frequency range encompassing the theta band (3–12 Hz) and, more importantly, are asymmetric between pairs of recording sites. Furthermore, we find that the degree of interaction decreases as a function of distance between electrode positions, suggesting that these interactions are a predominantly local phenomenon. Taken together, our results show that directed coupling measures based on MVAR models are able to provide important insights into the spatial and temporal formation of local functionally coupled ensembles during visual memory in V4. Moreover, our findings suggest that visual memory is accompanied not only by a temporary increase of oscillatory activity in the theta band, but by a direction-dependent change in theta coupling, which ultimately represents a change in functional connectivity within the neural circuit.

Time, frequency, and time‐varying Granger‐causality measures in neuroscience

“…This methodology consists in estimating VAR models in short temporal sliding windows where the underlying process is assumed to be (locally) stationary. See Ding et al for a methodological tutorial on windowing estimate in neuroscience and Long et al and Hoerzer et al for some applications in neuroscience.…”

Theta coupling between V4 and prefrontal cortex predicts visual short-term memory performance

“…Specifically, theta oscillations are enhanced during the delay period of memory tasks in both lPF and V4 (ref. 22), and increased oscillatory theta synchrony is accompanied by a phase-dependent coding of visual stimuli retained in short-term memory 23,24 .…”

Computational principles of microcircuits for visual object processing in the macaque temporal cortex

“…Granger causality states, based on linear regression modeling of time series, that if the current value of a time series A can be estimated more precisely by using the past values of both the time series A itself and another time series B than using only the past values of A, then signal B has a causal influence on signal A in Granger's sense. The concept of Granger causality has been extended to the frequency domain [94] and this analytical tool has been applied primarily to continuous signals in the neuroscience field [90,[95][96][97][98][99][100][101][102]. A recently developed nonparametric Granger causality analysis [103][104][105] has enabled the application of this method to spike data, which cannot be directly examined in the conventional Granger causality analysis due to discreteness (see also [106][107][108][109]).…”