Periodic fluctuations of neuronal activity, i.e. oscillations, have a functional role in visual perception, which is improved by covert attention (our ability to selectively process information at one location in the visual scene without eye movements). Oscillatory brain activity correlates with the engagement of visuospatial attention and influences performance in healthy observers. In neurological patients, abnormal oscillatory activity following brain damage accompanies visual impairments. However, no study has systematically manipulated either cor- tical oscillatory activity, or its interaction with covert attention, to improve visual performance in healthy adults, using Transcranial Magnetic Stimulation (TMS); a well-established, focal and non-invasive brain stimulation technique. This knowledge is important to improve perceptual function in healthy human observers and rehabil- itate faulty perception in patients. With healthy observers, we will use TMS rhythmic patterns to entrain local oscillatory activity in specific cortical sites alone and/or in combination with attention. We will assess whether the entrainment of oscillatory activity (i.e., phase alignment and increased power) facilitates contrast sensitivi- ty?a fundamental, well-understood visual dimension determining the window of visibility, which is increased by attention.
In Aim 1, we will test the ability of oscillation-tailored rhythmic TMS to improve visual performance, and record its time-frequency signature. We will apply either brief rhythmic active TMS or rhythmic sham (non- magnetic placebo) stimulation at the Alpha?10Hz and Beta?30Hz frequencies, at stimulus onset to two cortical areas involved in the modulation of perception and attention: right occipital (V1) and frontal (FEF) sites. We explore the effect of phase by manipulating the interval between display and TMS burst onsets. While manipu- lating phase, we will compare the impact of (a) rhythmic active vs. random active TMS (same pulse number and duration); (b) rhythmic sham vs. random sham stimulation; (c) rhythmic active TMS vs. rhythmic sham sti- mulation; (d) random active TMS vs. random sham stimulation, on threshold and asymptotic performance to assess changes in contrast gain and/or response gain.
In Aim 2, we will concentrate on the most effective cor- tical site-frequency-phase pattern combination found in Aim 1, as assessed by the size of the effects and con- sistency across observers, to test whether covert attention can potentiate such effects. We will manipulate ex- ogenous (involuntary, reflexive) attention, which is not cognitively demanding and has been well-characterized with psychophysics, neuroimaging and electrophysiology. By conducting concurrent TMS-EEG recordings while observers perform a discrimination task, we will increase our understanding of how the brain processes visual information, how the entrainment of neural activity is related to perceptual improvements, and how cov- ert attention affects spatial and temporal aspects of visual processing. In addition, this proposal will probe the feasibility of non-invasive neurostimulation combined with attentional manipulations to entrain brain oscillatory activity and improve visual function in healthy observers, and, in the future, restore vision in patients.
We will investigate the ability of rhythmic Transcranial Magnetic Stimulation (TMS) to entrain oscillatory brain activity, alone and in conjunction with attention, to improve visual perception. The proposed studies will advance our knowledge of how to improve perceptual function in healthy human observers, and probe the feasibility of using TMS techniques to rehabilitate faulty perception in patients.
