Ed Awh
Rhythmic brain activity tracks the content and timing of online spatial representations

A substantial body of evidence suggests that neural activity in the alpha frequency band (8-12 Hz) covaries with the locus of covert spatial attention, such that attention to one visual field yields a sustained decline in alpha power at contralateral electrode sites. In our work, we have exploited this covariation by using an inverted encoding model to reconstruct spatial response profiles (termed channel tuning functions, or CTFs) based on the topography of alpha activity on the human scalp. Thus, in a task that required the storage of locations in working memory, we observed a graded profile of activity across spatial channels that peaked at the stored location during both the encoding and delay periods of the task. These spatial CTFs provide an opportunity to quantify the basic tuning properties of online spatial memories to examine how the precision of neural representations changes with manipulations of the probability of storage or the number of items stored. In addition, I'll show that the same method can be used to track the locus and timing of covert attention following the presentation of symbolic orienting cues and during active visual search. Moreover, we demonstrate that dynamic changes in the selectivity of spatial CTFs provide a sensitive measure of the latency of covert orienting during visual search. These findings demonstrate the integral role that alpha band activity plays in the online representation of space, and provide a powerful new approach for tracking these representations during online storage and covert orienting.