TMS as a Biological Marker of Neuroplasticity

Aphasia is an impairment of language that may occur after a stroke (or other brain injuries). A person with aphasia may experience difficulties speaking, understanding speech, reading, writing, or any combination of these symptoms. Despite advances in understanding of language systems and functional neuroplasticity after brain injury, accurate predictors of aphasia recovery after stroke remain elusive. In order to better understand, predict, and enhance language improvement after stroke, there is a critical need to develop tools that can assess the influence of neuroplasticity on recovery.

Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation tool that has been used to predict the brain's neuroplastic capacity by assessing physiological responses observed immediately following administration of TMS. Additionally, difference in the physiological response to TMS have been shown to be affected by polymorphism in the gene coding for brain derived neurotrophic factor (BDNF). The current project explores the idea that because neural mechanisms of plasticity are essential determinants of both recovery after brain injury and physiologic response to TMS, magnetic brain stimulation could be employed as an indicator of the capacity for clinically relevant neuroplasticity, and potentially as a predictor of recovery from post-stroke deficits such as aphasia

The goals of this protocol are to 1) explore the utility of theta burst stimulation (TBS), a type of transcranial magnetic stimulation (TMS), as a tool for assessing neuroplasticity in the language system in patients with aphasia due to stroke, 2) and to assess the utility of TBS as a biomarker and predictor of functional recovery in patients with aphasia.

This protocol will encompass two separate but related experiments. In the first experiment, the investigators will apply TBS to brain regions that control language functions in aphasic patients in order to determine whether we can induce a transient improvement in naming ability. They will use a statistical model they have developed to categorize patients as either having High Plasticity or Low Plasticity. The investigators will determine whether this distinction predicts which patients are likely to have greater TBS-induced changes in language performance. In the second experiment, in the same patients, the investigators will apply TBS to the motor cortex to elicit changes in motor evoked potentials (MEPs). Using the same model to form matched groups, we predict that MEPs will be more attenuated in High Plasticity groups compared to the Low Plasticity group.