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.

Inclusion Criteria:

- Must have Aphasia due to stroke

- Stroke must have occurred at least 6 months ago

- Native English speaker

- Willing & able to have a MRI

Exclusion Criteria:

- Disorders of the brain other than stroke (i.e. tumor, Parkinsons, cancer... etc.)

- History of seizures/ or epilepsy

- Pacemaker or other implanted electronic devices

- Consumption of medications that lower seizure threshold

- History of psychiatric disorders

- History of tinnitus

- Current abuse of drugs or alcohol

- Pregnant or plan to get pregnant