Top-down Memory Signal from Frontal Cortex Modulates Activities within Extrastriate Cortex

Background and Aim : We have recently shown that in the absence of firing rate changes, a spatially specific working memory (WM) signal drives subthreshold modulations in visual areas. This subthreshold input results in enhanced visual processing. Furthermore, we have revealed that neurons in extrastriate visual areas receive a strong top-down signal from frontal eye field (FEF) during the maintenance of spatial information. Here, we sought to study the role of FEF in the enhancement of visual information within the extrastriate cortex during WM.Methods : We pharmacologically inactivated FEF and simultaneously recorded the spiking activity and local field potentials from multiple sites within the V4 cortex during a modified version of the memory-guided saccade task. In this task, a set of grating bars, with different contrasts and orientations, were presented as a background on the screen throughout the task. The FEF inactivation was done by injecting a small amount of muscimol in an overlapping area between FEF motor field and v4 receptive filed (RF).Results : The FEF inactivation diminished the behavioral performance as well as increased the saccade errors and reaction times of monkeys in the location corresponding to the injected area. Neural processing, based on the area under ROC, had shown no memory-related change in the firing rate while the LFP signals indicated spatial modulation (inside vs. outside the RF) during WMConclusion : Together, these findings indicate that the WM induced enhancement of the visual representation by recruitment of alpha-beta oscillation is controlled from FEF. These results provide a mechanistic understanding of how a spatially specific WM signal from prefrontal cortex is capable of changing visual information within extrastriate cortex to enhance the visual discrimination performance.

کلیدواژه ها:

Frontal Eye Field ، muscimol inactivation ، top-down process ، V4 area ، working memory