Distinctive nonlinear dimensionality of neural spiking activity in extrastriate cortex during spatial working memory; a Higuchi fractal analysis

Working memory serves as a basis for many cognitive functions, including attention, decision-making, and learning. When engaged, it is often associated with an increase in the average neural firing rates across different sensory and sensorimotor regions of the brain. However, a modulation of the neural firing rate in extrastriate cortex, involved in visual processing, has never been reported during the maintenance of visual information. Here, for the first time, we show that despite the absence of a modulation in the firing rate of the neurons in the middle temporal cortex (part of extrastriate cortex), their nonlinear dimensionality, captured by the Higuchi method, is increased when the locus of spatial working memory corresponds with the neurons' receptive field. Our finding sheds more light on the neural mechanisms of working memory and would help diagnosis processes of cognitive disorders that are thought to be rooted in a malfunctioning working memory. It also calls attention toward the need for novel approaches toward studying the neural activities beyond a modulation in the average discharge rate.