ABSTRACT
We aimed to identify neuroanatomical regions associated with deficits to the graphemic buffer, a working memory component of the spelling system that holds the sequence of letter identities during production. We evaluated 331 patients with left hemisphere ischemic stroke with various spelling tests and magnetic resonance diffusion-weighted imaging and perfusion-weighted imaging, within 48 hours of stroke onset. A voxel-wise statistical map showed that ischemia in voxels in posterior and inferior frontal and parietal cortex, subcortical white matter underlying prefrontal cortex, lateral occipital gyrus, or caudate was associated with impairment in maintaining the sequence of letter identities while spelling.
Subject(s)
Brain Ischemia/physiopathology , Brain/physiopathology , Linguistics , Memory, Short-Term/physiology , Stroke/physiopathology , Writing , Analysis of Variance , Diffusion Magnetic Resonance Imaging , Female , Humans , Language Tests , Magnetic Resonance Angiography , Male , Middle Aged , Neuropsychological Tests , Time FactorsABSTRACT
A number of previous studies have indicated that Broca's area has an important role in understanding and producing syntactically complex sentences and other language functions. If Broca's area is critical for these functions, then either infarction of Broca's area or temporary hypoperfusion within this region should cause impairment of these functions, at least while the neural tissue is dysfunctional. The opportunity to identify the language functions that depend on Broca's area in a particular individual was provided by a patient with hyperacute stroke who showed selective hypoperfusion, with minimal infarct, in Broca's area, and acutely impaired production of grammatical sentences, comprehension of semantically reversible (but not non-reversible) sentences, spelling, and motor planning of speech articulation. When blood flow was restored to Broca's area, as demonstrated by repeat perfusion weighted imaging, he showed immediate recovery of these language functions. The identification of language functions that were impaired when Broca's area was dysfunctional (due to low blood flow) and recovered when Broca's area was functional again, provides evidence for the critical role of Broca's area in these language functions, at least in this individual.
Subject(s)
Aphasia, Broca/physiopathology , Diffusion Magnetic Resonance Imaging , Frontal Lobe/blood supply , Frontal Lobe/physiopathology , Image Processing, Computer-Assisted , Imaging, Three-Dimensional , Magnetic Resonance Angiography , Speech Production Measurement , Acute Disease , Aged , Aphasia, Broca/diagnosis , Aphasia, Broca/therapy , Blood Flow Velocity/drug effects , Blood Flow Velocity/physiology , Brain Mapping , Combined Modality Therapy , Hemodilution , Heparin/therapeutic use , Humans , Infarction, Middle Cerebral Artery/diagnosis , Infarction, Middle Cerebral Artery/physiopathology , Infarction, Middle Cerebral Artery/therapy , Male , Mutism/diagnosis , Mutism/physiopathology , Mutism/therapy , Neuropsychological Tests , Regional Blood Flow/drug effects , Regional Blood Flow/physiology , SemanticsABSTRACT
Spatial processing was assessed following implantation of subdural electrodes in the nondominant hemisphere with electrocortical stimulation mapping (ESM) in two patients before epilepsy surgery. The first patient had mild hemispatial neglect/extinction during ESM of posterior temporal and inferior parietal areas. These areas were resected, and the patient had postoperative deficits that were similar to those occurring with ESM. The second patient was found to have marked hemispatial neglect during stimulation of parietal areas. These areas were not resected, and the patient had no neglect following surgery. These results suggest that ESM can help predict spatial processing deficits associated with cortical resection, and may help prevent postoperative impairments following resection in right parietal or temporal regions.
