http://stroke.ahajournals.org/content/48/3/820?etoc=
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Introduction
Transcranial
direct current stimulation (tDCS), a form of noninvasive brain
stimulation originally studied for its effect on motor limb physiology,1 has been investigated for its use in the treatment of aphasia since 2008.2–3
The experimental use of tDCS for aphasia, however, began differently
from those paradigms established for poststroke motor recovery, both
conceptually and in method. Not only is aphasia research a relative
newcomer to the field of tDCS experimentation, it has thus far been
somewhat of an outlier in its limited use of tDCS autonomously.
Theoretically
understood to be vastly more complex than our intricate motor systems,
cortical language representation has most recently been conceptualized
as a dual stream, diffuse network,4–6 with language processing subcomponents evolved from nonlinguistic primates.7,8
In the dual stream model, human language functions are lateralized
primarily in the left hemisphere, with Broca’s area comprising the left
complement of a bilateral dorsal stream network devoted to naming and
articulation. Conversely, Wernicke’s area constitutes the origin of a
bilateral ventral stream in which semantic meaning is attached to
components of speech sounds.6,9–21
Additional activation in homologous right hemisphere language areas
seems to be determined by lexical necessity, with increased articulatory
demands activated within the bilateral dorsal stream and the decoding
of unfamiliar words activated in the bilateral ventral stream network.9
Complex as it may be to optimally prime the motor cortex for poststroke
limb rehabilitation using tDCS, it may be considered even more
challenging to modulate the cortical plexus which encodes and produces
language in all of its richness. The theoretical mechanisms of brain
activation during tDCS protocols suggest that tDCS primes the brain for
enhanced outcomes in behavioral therapies,22 which may have led to the appeal of combining methods concurrently. The …
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