The turtle visual system mediates a complex spatiotemporal transformation of visual stimuli into cortical activity

Abstract

The three-layered visual cortex of turtle is characterized by extensive intracortical axonal projections and receives non-retinotopic axonal projections from lateral geniculate nucleus. What spatiotemporal transformation of visual stimuli into cortical activity arises from such tangle of malleable cortical inputs and intracortical connections? To address this question, we obtained band-pass filtered extracellular recordings of neural activity in turtle dorsal cortex during visual stimulation of the retina. We discovered important spatial and temporal features of stimulus-modulated cortical local field potential (LFP) recordings. Spatial receptive fields span large areas of the visual field, have an intricate internal structure, and lack directional tuning. The receptive field structure varies across recording sites in a distant-dependent manner. Such composite spatial organization of stimulus-modulated cortical activity is accompanied by an equally multifaceted temporal organization. Cortical visual responses are delayed, persistent, and oscillatory. Further, prior cortical activity contributes globally to adaptation in turtle visual cortex. In conclusion, these results demonstrate convoluted spatiotemporal transformations of visual stimuli into stimulus-modulated cortical activity that, at present, largely evade computational frameworks.

Dynamics and sources of response variability and its coordination in visual cortex

“…Second, for the sake of experimental practicality and stable monitoring of cortical population activity, we chose to employ LFP recordings using a microelectrode array inserted into the geniculo-recipient dorsal cortex (visual cortex) of the turtle eye-attached whole-brain ex vivo preparation (Shew et al, 2015; Clawson et al, 2017; Hoseini et al, 2017 a , b ). Both synaptic currents and spikes from many neurons within a volume around the recording electrode contribute to the LFP signal (Lindén et al, 2011; Buzsáki et al, 2012).…”