Local field potentials reflect multiple spatial scales in V4

Abstract

Local field potentials (LFP) reflect the properties of neuronal circuits or columns recorded in a volume around a microelectrode (Buzsáki et al., 2012). The extent of this integration volume has been a subject of some debate, with estimates ranging from a few hundred microns (Katzner et al., 2009; Xing et al., 2009) to several millimeters (Kreiman et al., 2006). We estimated receptive fields (RFs) of multi-unit activity (MUA) and LFPs at an intermediate level of visual processing, in area V4 of two macaques. The spatial structure of LFP receptive fields varied greatly as a function of time lag following stimulus onset, with the retinotopy of LFPs matching that of MUAs at a restricted set of time lags. A model-based analysis of the LFPs allowed us to recover two distinct stimulus-triggered components: an MUA-like retinotopic component that originated in a small volume around the microelectrodes (~350 μm), and a second component that was shared across the entire V4 region; this second component had tuning properties unrelated to those of the MUAs. Our results suggest that the LFP reflects neural activity across multiple spatial scales, which both complicates its interpretation and offers new opportunities for investigating the large-scale structure of network processing.

Coherent alpha oscillations link current and future receptive fields during saccades

“…Two monkeys (Macaca fascicularis, both female) were subjects in the experiments. The recording methods have been described previously (14,17,19). Briefly, a sterile surgical procedure was carried out to implant a head-post, after which monkeys were trained to make visually guided saccades for liquid rewards.…”

“…Thus, perisaccadic changes in current-future field alpha coherence were robust to different analysis time windows and saccade vectors. Because these coherence changes were specific to the currentfuture field electrode pairs, they could not be attributed to a global synchronization of LFP signals across V4 (17) or to nonspecific visual landmarks. We therefore focused our remaining analyses on this frequency band.…”

“…2A shows the layout for the array in monkey N, with each blue dot indicating the center of the receptive field measured at a single electrode. We used the LFPs to define receptive field locations, based on previous observations that LFP retinotopy in V4 closely matches the retinotopy of spiking activity (17). For a 10°leftward saccade, a neuron with a receptive field centered at the blue dot ( Fig.…”

“…LFP receptive field center estimation. We used a method defined previously (17) to extract the retinotopic component of the LFP. Briefly, a generative model was fitted to the data to capture the retinotopic and global components of LFP responses to stimuli flashed at multiple locations on the screen.…”

Models of Neuronal Stimulus-Response Functions: Elaboration, Estimation, and Evaluation

“…The assumption of Gaussian response noise is inappropriate for single-trial spike counts, although it may be better motivated when the responses being modeled are trial-averaged mean rates (Theunissen et al, 2000; Linden et al, 2003), subthreshold membrane potentials (Machens et al, 2004), local field potentials (Mineault et al, 2013), or intracranial electrocorticographical recordings (Mesgarani and Chang, 2012); but even then the assumption of constant variance may be violated. Instead, the value of the probabilistic interpretation lies in access to a principled theory of stabilized (or “regularized”) estimation, and to the potential generalization to nonlinear and non-Gaussian modeling assumptions, both of which we discuss below.…”