الفهرس 
Brain: Visual cortexOnly 14 pages are availabe for public view
 |  | from | 208 |  |  |
| | | from | 208 | | |
Abstract
Dysphasia, a condition defined as the partial or complete loss of
language function after brain damage, is one of the most devastating
cognitive deficits produced by stroke lesions. Over the past decades, there
have been great advances in the diagnosis and treatment of post-stroke
language and communication deficits. In particular, the advent of
functional brain imaging and other brain mapping methods has advanced
our understanding of how the intact and lesioned brain takes over the
activity of irretrievably damaged networks in dysphasic patients.
Right hemisphere (RH) regions contralateral to the dysphasiainducing
lesion may be recruited to support recovery of language. Several
variables affect language recovery–related neuroplastic processes,
including patient variables. Patients vary with regard to lesion
characteristics and the language deficits that they present. Lesions may
extend beyond their structural boundaries, and we therefore recommend
using perfusion imaging as well as structural imaging to determine the
dimensions of the lesion and, in turn, to determine candidate tissue for
recovery. Because it is possible that damage to white matter connections
may play a role in dysphasia recovery, we recommend that future studies
of language recovery use diffusion tensor imaging to evaluate the
integrity of these pathways.
Dysphasia following a right hemisphere lesion (crossed dysphasia)
in right-handed individuals is rare, most studies shows a prevalence of
less than 3%. Two studies reported an increased incidence of about 20%
to 25% for language deficits in left- or non-right-handers after right
hemispheric stroke. Another study found no such increase and suggested
a negligible role of the right hemisphere in speech function in most leftSummary
and Conclusions
128
handers without a history of early left-hemisphere damage. Only 38% of
hemispheric lesions in the language dominant hemisphere will result in
transient, and 18% in permanent dysphasia. Difficulties in the assessment
of language performance due to physical exhaustion and deficits in
attention in the early stages after stroke and restitution in the later stages
may have led to an under diagnosis of dysphasia in right-hemispheric
stroke patients. Another shortcoming of studies on differences in
dysphasia incidences in left- and right-handers is the small number of lifthanders
with right-hemispheric stroke and dysphasia. Additionally,
patients with language disturbances after cerebral infraction do not
infrequently have pre-existing lesions in the other hemisphere rendering
conjectures on the original hemispheric language dominance ambiguous.
In addition, patients with crossed dysphasia often have subcortical
lesions instead of lesions of classical language areas.
Previous research data suggest that the right hemisphere participate
in language recovery and treatment gains in dysphasia. In cases of large
lesions and poorer recovery, right-hemisphere activity is prominent. The
fact that recovery in these cases is poor does not indicate that the right
hemisphere is not useful for or necessarily interferes with language
processes. Rather, it suggests that right-hemisphere structures are most
active when left-hemisphere structures are so damaged that they are not
adequate for the task. It is possible that activity in both hemispheres of
dysphasia patients interferes with language processes, depending on the
patient, the size of the lesion, and the severity of dysphasia. Evidence
suggests that silencing such extraneous activity in either hemisphere will
have a positive impact on treatment.
Previous findings suggest that lateralization of brain processes
related to language is not entirely a passive process, but can be influenced
Summary and Conclusions
129
by manipulation of attention. Initial findings indicate that pairing an
intention manipulation (complex left-hand movement) with picture
naming during treatment has a positive impact on outcome and shifts
lateral frontal activity toward the right hemisphere. However, these data,
especially the fMRI data, should be considered preliminary at this point
in time. Much work has to be done before the full impact of this
manipulation on treatment can be assessed. For example, it is unknown
how much the complex left-hand movement contributes to treatment
outcome and re-lateralization of lateral frontal activity to the right
hemisphere.
Several studies are currently conducting a study to address these
questions. Another question that should be addressed is whether the
intention manipulation can enhance the effects of other treatment
manipulations. Hence, there is much work to be done before we
completely understand the potential contributions of the intention
component to treatment outcome.
At the beginning of this essay, I noted that two simple, related
assumptions regarding the development of new treatments for dysphasia.
The first was that dysphasia researchers and clinicians can develop
treatments to engage specific neural substrates in the service of dysphasia
rehabilitation. Implementing this conceptually driven method requires
that was learn a great deal more than currently know about the neural
substrates of treatment and recovery of function in dysphasia. Doing so
will require increasing investment in functional imaging studies. The
second, related assumption was that dysphasia researchers can use
functional brain imaging to ascertain whether treatments developed in
this fashion actually engage the targeted substrates. The findings
regarding to the novel intention treatment are promising in this regard.
Summary and Conclusions
130
This treatment was developed to help patients with nonfluent dysphasia
focus word production mechanisms in the right lateral frontal lobe.
CONCLUSION
To date, functional imaging data suggest that all studies and
researches have been successful in accomplishing this goal. More
importantly, the data suggest that fMRI and other functional imaging
modalities can be a powerful tool in developing conceptually driven
treatments for dysphasia that target specific neuroplastic substrates.
Findings from functional imaging can be used to verify the conceptual
basis of the treatment and to guide further development