UC Berkeley

Since early recordings of the human brain, rhythmic electric fields have been observed emanating from regions involved in the specific information processing demands of which the human subject is engaged. Different oscillatory frequencies have been associated with different types of information processing. Neuroscience in the 21st century has seen a revival in research studying the neural basis of oscillatory activity that has deepened our understanding of the complex network level coordination of brain regions. However, causal evidence for the mechanistic role of neural oscillations is sparse, yet provides vital implications for the neural basis of cognition.

The first experiment examines the specific role of beta (15-30 hertz) and gamma (30-50 hertz) frequency oscillations in top-down and bottom-up attention. By applying rhythmic transcranial magnetic stimulation (TMS), the purported cognitive contributions of beta and gamma oscillations are analyzed with respect to a visual search task that varies the level of top-down attention required for optimal performance.

The second experiment examines the specific role of theta (3-8 hertz) and alpha (8-12 hertz) frequency neural oscillations in the reactivation and suppression of working memory representations. Rhythmic TMS in a retro-cued delayed match-to-sample task causally tested previously reported oscillatory neural signatures for their mechanistic contributions to working memory. The degree to which subjects engaged the regions targeted by TMS in functional magnetic resonance imaging (fMRI) predicted the frequency specific effect of rhythmic TMS.

Simultaneous TMS and fMRI offers a unique opportunity to causally test the communication through coherence proposed with neural oscillations. By stimulating a single brain region in multiple frequency bands, the frequency-by-network specific spread of activation can be quantified. Towards this end, the third experiment develops the methodology of concurrent TMS-fMRI with a proof of principle experiment demonstrating the spread of TMS effects through a functional network. In sum, these projects test for the causal role of neural oscillations in cognition and pave the way for future research to study the network level organization of the brain via neural oscillations.