Variability in blood oxygen level dependent (BOLD) signal in patients with stroke-induced and primary progressive aphasia.

Although fMRI is increasingly used to assess language-related brain activation in patients with aphasia, few studies have examined the hemodynamic response function (HRF) in perilesional, and contralesional areas of the brain. In addition, the relationship between HRF abnormalities and other variables such as lesion size and severity of aphasia has not been explored. The objective of this study was to investigate changes in HRF signal during language-related neural activation in patients with stroke-induced aphasia (SA). We also examined the status of the HRF in patients with aphasia due to nonvascular etiology, namely, primary progressive aphasia (PPA). Five right handed SA patients, three PPA patients, and five healthy individuals participated in the study. Structural damage was quantified with T1-weighted MR images. Functional MR imaging was performed with long trial event-related design and an overt naming task to measure BOLD signal time to peak (TTP) and percent signal change (ΔS). In SA patients, the average HRF TTP was significantly delayed in the left hemisphere regions involved in naming compared to healthy participants and PPA patients. However, ΔS was not different in SA patients compared to the other two groups. Delay in HRF TTP in the left hemisphere naming network of SA patients was correlated with lesion size and showed a negative correlation with global language function. There were no significant differences in the HRF TTP and ΔS in the right hemisphere homologues of the naming network or in the left and the right occipital control regions across the three groups. In PPA patients, HRF had a normal pattern. Our results indicate that abnormal task-related HRF is primarily found in the left hemisphere language network of SA patients and raise the possibility that abnormal physiology superimposed on structural damage may contribute to the clinical deficit. Follow-up investigations in a larger sample of age-matched healthy individuals, SA, and PPA patients will be needed to further confirm and extend our findings.

Writing with the right hemisphere.

We studied writing abilities in a strongly right-handed man following a massive stroke that resulted in virtually complete destruction of the language-dominant left hemisphere. Writing was characterized by sensitivity to lexical-semantic variables (i.e., word frequency, imageability, and part of speech), semantic errors in writing to dictation and written naming, total inability to use the nonlexical phonological spelling route, and agrammatism in spontaneous writing. The reliance on a lexical-semantic strategy in spelling, semantic errors, and impaired phonology and syntax were all highly consistent with the general characteristics of right hemisphere language, as revealed by studies of split-brain patients and adults with dominant hemispherectomy. In addition, this pattern of writing closely resembled the syndrome of deep agraphia. These observations provide strong support for the hypothesis that deep agraphia reflects right hemisphere writing.

Memory impairment and executive control in individuals with stroke-induced aphasia.

The purpose of this study was to examine memory abilities of aphasic individuals in relation to site of neurological lesion. Fourteen individuals with stroke-induced aphasia (7 with anterior lesions; 7 with posterior lesions) and 14 demographically matched control subjects were given selected tests of short-term memory (STM) and long-term memory (LTM). Stroke patients were impaired relative to control subjects on tests of verbal memory, with greater impairment of LTM associated with anterior lesions and greater impairment of STM associated with posterior lesions. Verbal memory performance did not correlate highly with language ability, and did not appear to be simply a consequence of language impairment. Executive control deficits were postulated as explanatory of the LTM impairment associated with anterior lesions.

Auditory processing in individuals with mild aphasia: a study of resource allocation.

This study examined the effects of lesion location (frontal vs. posterior) and nature of distraction (nonverbal vs. verbal secondary, competing task) on mildly aphasic individuals' performances of listening tasks that required semantic judgments and lexical decisions under isolation, focused attention, and divided attention conditions. Despite comparable accuracy among all groups during isolation conditions, the aphasic groups responded less accurately and more slowly than the normal control group during focused and divided attention conditions. Generally, the two aphasic groups performed similarly, quantitatively and qualitatively. Demographic characteristics such as time post stroke did not correlate with performance decrements. Independent of group, all individuals showed greater disruption of auditory processing skills when the secondary task was verbal rather than nonverbal. Within a limited-capacity model of attention, the results suggest that aphasic individuals display impairments of attention and resource allocation and that these impairments negatively interact with their auditory processing abilities.

Spoken language of individuals with mild fluent aphasia under focused and divided-attention conditions.

The spoken language of individuals with mild aphasia and age-matched control subjects was studied under conditions of isolation, focused attention, and divided attention. A picture-description task was completed alone and in competition with a tone-discrimination task. Regardless of condition, individuals with aphasia performed more poorly on most morphosyntactic, lexical, and pragmatic measures of spoken language than control subjects. Increasing condition complexity resulted in little quantitative or qualitative change in the spoken language of the control group. In contrast, the individuals with aphasia showed dual-task interference; as they shifted from isolation to divided-attention conditions, they produced fewer syntactically complete and complex utterances, fewer words, and poorer word-finding accuracy. In pragmatic terms, their communication was considered less successful and less efficient. These results suggest that decrements of attentional capacity or its allocation may negatively affect the quantity and quality of the spoken language of individuals with mild aphasia.

Examining the value of lexical retrieval treatment in primary progressive aphasia: two positive cases.

Individuals with primary progressive aphasia (PPA) suffer a gradual decline in communication ability as a result of neurodegenerative disease. Language treatment shows promise as a means of addressing these difficulties but much remains to be learned with regard to the potential value of treatment across variants and stages of the disorder. We present two cases, one with semantic variant of PPA and the other with logopenic PPA, each of whom underwent treatment that was unique in its focus on training self-cueing strategies to engage residual language skills. Despite differing language profiles and levels of aphasia severity, each individual benefited from treatment and showed maintenance of gains as well as generalization to untrained lexical items. These cases highlight the potential for treatment to capitalize on spared cognitive and neural systems in individuals with PPA, improving current language function as well as potentially preserving targeted skills in the face of disease progression.

Acquired alexia: lessons from successful treatment.

Two individuals with anomic aphasia and acquired alexia were each provided treatment for their reading impairment. Although reading of single words in isolation was fairly accurate, their text reading was slow and effortful, including functor substitutions and semantic errors. Prior to treatment, reading reaction times for single words showed grammatical class and word-length effects. Both patients responded positively to a treatment protocol that included two phases: (1) multiple oral rereading of text, and (2) reading phrase-formatted text that had increased spacing between phrasal clauses. Their reading rates for text improved while maintaining good comprehension. Following treatment, reading reaction times for single words showed the elimination of grammatical class and word-length effects, suggesting improved access to word forms, particularly functors.

Praxis and the right hemisphere.

We report our observations on praxis in a strongly right-handed man following a massive stroke that resulted in virtually complete destruction of the left cerebral hemisphere. Our patient was severely impaired in pantomiming transitive gestures with the left hand and in reproducing novel non-symbolic hand and arm movement sequences. However, overlearned habitual actions like actual object use and intransitive gestures were relatively spared. Performance of axial commands was intact. Gesture recognition and discrimination were also preserved. Based on these findings, we propose that the praxis system of the right hemisphere is strongly biased toward "concrete" or context-dependent execution of familiar, well-established action routines. The right hemisphere is critically dependent on transcallosal contribution from the left hemisphere for control of the left hand in "abstract" or context-independent performance of transitive movements and in learning novel movement sequences. At least in some individuals, the right hemisphere can recognize and discriminate gestures. Possible implications of our findings for the cerebral control of praxis and for recovery from apraxia are discussed.