State-dependency in brain stimulation studies of perception and cognition

We address the importance of understanding initial states of neuronal populations and of state-dependent responses in cognitive neuroscience experiments with special emphasis on brain stimulation studies of perception and cognition. The approach we present is based on evidence that behavioural and perceptual effects of transcranial magnetic stimulation (TMS) are determined by initial neural activation state; by systematically manipulating neural activation states before application of TMS, one can selectively target specific, even spatially overlapping neural populations within the affected region. This approach is potentially of great benefit to cognitive neuroscience and remediation programmes as it combines high spatial and functional resolution with the ability to assess causality. We address the importance of understanding initial states of neuronal populations and of state-dependent responses in cognitive neuroscience experiments with special emphasis on brain stimulation studies of perception and cognition. The approach we present is based on evidence that behavioural and perceptual effects of transcranial magnetic stimulation (TMS) are determined by initial neural activation state; by systematically manipulating neural activation states before application of TMS, one can selectively target specific, even spatially overlapping neural populations within the affected region. This approach is potentially of great benefit to cognitive neuroscience and remediation programmes as it combines high spatial and functional resolution with the ability to assess causality. reduction of response to a sensory stimulus induced by repeated presentation of that stimulus. the measurement of electrical activity produced by the brain as recorded from electrodes placed on the scalp. in offline paradigms, a longer lasting (up to an hour) suppression of neural activity is induced with rTMS before subjects perform a behavioural task. single pulse (or brief pulse trains of) TMS applied during a behavioural task. subjective experience of flashes of light that can be induced by application of TMS over the visual cortex. the application of weak electrical currents (1-2 mA) to modulate the activity of neurons in the brain non-invasive method for modulating neural activity by weak electric currents induced by rapidly changing magnetic fields.