Acquisition of novel semantic information in amnesia: effects of lesion location

Two patients with severe global amnesia are described who differ in the extent to which they have acquired new semantic information. Patient SS, who has extensive medial temporal lobe damage including the hippocampus as well as surrounding cortical areas, has failed to acquire virtually any new information regarding vocabulary or famous faces that entered the public domain since the onset of his amnesia. In contrast, patient PS, who has a selective lesion of the hippocampus proper, has gained a sense of familiarity of novel vocabulary and famous people, even though her effortful retrieval of this new semantic knowledge remains impaired. These findings extend to amnesia of adult onset, the proposal of Vargha-Khadem and colleagues that in patients with selective hippocampal injury, cortical areas surrounding the hippocampus may play an important role in new semantic learning [Vargha-Khadem, F., Gadian, D.G., Watkins, K. E., Connelly, A., Van Paesschen, W. and Mishkin, M., regarding the importance of the subhippocampal cortices in the mediation of new semantic learning in children with hippocampal lesions, Science, 1997, 277, 376-380].

Dissociation of attentional processes in patients with focal frontal and posterior lesions

A location-based ('select-what, respond-where') priming task was used to examine three measures of selective attention (interference (INT), negative priming (NP), and inhibition of return (IOR)) as a function of focal brain pathology and the complexity of target selection. Control subjects showed different patterns of performance for the three attentional measures as a function of complexity, suggesting some independence among INT, NP, and IOR. Brain-damaged subjects showed significant response slowing, as well as a number of lesion-specific attentional abnormalities. Right frontal (including bifrontal) damage resulted in proportionally increased interference related to task complexity. Left posterior damage increased IOR in the most complex task, while left frontal damage reversed the control pattern of IOR as a function of complexity. Right hemisphere (right posterior and right frontal damage) pathology resulted in a virtual loss of negative priming at all levels of task complexity; left and bifrontal damage resulted in diminished NP only related to increases in the complexity of selection. INT, NP, and IOR are mediated by different brain regions and their expression can be modulated by the complexity of the selection task.

Lesion site patterns in severe, nonverbal aphasia to predict outcome with a computer-assisted treatment program

OBJECTIVE

To test whether lesion site patterns in patients with chronic, severe aphasia who have no meaningful spontaneous speech are predictive of outcome following treatment with a nonverbal, icon-based computer-assisted visual communication (C-ViC) program.

DESIGN

Retrospective study in which computed tomographic scans performed 3 months after onset of stroke and aphasia test scores obtained before C-ViC therapy were reviewed for patients after receiving C-ViC treatment.

SETTING

A neurology department and speech pathology service of a Department of Veterans Affairs medical center and a university aphasia research center.

PATIENTS

Seventeen patients with stroke and severe aphasia who began treatment with C-ViC from 3 months to 10 years after onset of stroke.

MAIN OUTCOME MEASURE

Level of ability to use C-ViC on a personal computer to communicate.

RESULTS

All patients with bilateral lesions failed to learn C-ViC. For patients with unilateral left hemisphere lesion sites, statistical analyses accurately discriminated between those who could initiate communication with C-ViC from those who were only able to answer directed questions. The critical lesion areas involved temporal lobe structures (Wernicke cortical area and the subcortical temporal isthmus), supraventricular frontal lobe structures (supplementary motor area or cingulate gyrus 24), and the subcortical medial subcallosal fasciculus, deep to the Broca area. Specific lesion sites were also identified for appropriate candidacy for C-ViC.

CONCLUSIONS

Lesion site patterns on computed tomographic scans are helpful to define candidacy for C-ViC training, and to predict outcome level. A practical method is presented for clinical application of these lesion site results in combination with aphasia test scores.

Clustering and switching on verbal fluency: the effects of focal frontal- and temporal-lobe lesions

We examined the hypothesis that, on verbal fluency, clustering (i.e. generating words within subcategories) is related to temporal-lobe functioning, whereas switching (i.e. shifting between subcategories) is related to frontal-lobe functioning. Tests of phonemic and semantic fluency were administered to 53 patients with focal frontal-lobe lesions (FL), 23 patients with unilateral temporal-lobe lesions (TL) and 55 matched controls. Performance by FL patients was consistent with our hypothesis: in comparison to controls, patients with left-dorsolateral or superior-medial frontal lesions switched less frequently and produced normal cluster sizes on both phonemic and semantic fluency. Performance by TL patients was not consistent across fluency tasks and provided partial support for our hypothesis. On phonemic fluency, TL patients were unimpaired on both switching and clustering. On semantic fluency, TL patients were impaired on switching in comparison to controls and left TL patients produced smaller clusters than right TL patients. The best indices for discriminating the patient groups, therefore, were phonemic-fluency switching (impaired only with frontal lesions) and semantic-fluency clustering (impaired only with temporal-lobe lesions).

The effects of focal anterior and posterior brain lesions on verbal fluency

Seventy-four patients with focal brain lesions were compared to a neurologically normal control group on tasks of letter-based and category-based list generation. When patients were divided only by right frontal, left frontal, or nonfrontal lesion sites, the pattern of fluency impairments confirmed prior claims. When more precise lesion sites within the frontal lobes were compared between groups classified based on their fluency performance, much more specific brain-behavior relations were uncovered. Damage to the right dorsolateral cortical or connecting striatal regions, the right posterior area, or the medial inferior frontal lobe of either hemisphere did not significantly affect letter-based fluency performance. Superior medial frontal damage, right or left, resulted in moderate impairment. Patients with left dorsolateral and/or striatal lesions were most impaired. Left parietal damage led to performance relatively equivalent to the superior medial and left dorsolateral groups. The same lesion sites produced impairments in category based fluency, but so did lesions of right dorsolateral and inferior medial regions. Task analysis and correlations with other measures revealed that different cognitive processes related to different brain regions underlie performance on verbal fluency tests.

The effects of focal and diffuse brain damage on strategy application: evidence from focal lesions, traumatic brain injury and normal aging

A new test of strategy application was designed to be relatively free of the constraints that limit the standard neuropsychological assessment of supervisory abilities. The validity of the test was assessed in 3 samples of participants with varying degrees of supervisory deficits and frontal systems dysfunction: focal frontal lesions, traumatic brain injury (TBI), and normal aging. Inefficient strategy application varied systematically across the 3 groups and was not due to extraneous factors such as forgetting the test instructions. Previous case studies have emphasized strategy application deficits in the face of normal neuropsychological test performance. In this study, it was shown that strategically impaired participants from a consecutive series can include those both with and without deficient neuropsychological test performance. When neuropsychological impairment was present, it was greatest on executive functioning tasks. Among participants with nonstrategic performance, there was evidence for a dissociation of knowledge from action. This finding was not specific to focal frontal lesions. A number of supervisory processes contributing to strategy application were identified. Exploratory analyses indicated differential effects of lesion location on these processes, especially inferior medial frontal and right hemisphere lesions. Overall, the results supported the use of unstructured tasks in the assessment of supervisory abilities.

Recovery of arm function in patients with paresis after traumatic brain injury

OBJECTIVE

To characterize the frequency of recovery of arm paresis in patients with traumatic brain injury (TBI) admitted to rehabilitation.

DESIGN

Retrospective review identifying a cohort of patients with moderate or severe arm paresis after TBI followed at least 6 months postinjury.

SETTING

Freestanding acute rehabilitation hospital TBI unit.

PATIENTS AND METHODS

Forty-four patients with moderate to severe arm paresis were selected from 264 consecutive admissions and characterized by injury pathology subtype, injury severity (duration of unconsciousness [loss of consciousness, LOC] and posttraumatic amnesia [PTA]), age, and level of paresis according to Brunnstrom Stages of Recovery (BS 1 to 6). Patient groups with and without arm paresis were compared according to these variables (t tests and chi(2)).

MAIN OUTCOME MEASURES

Recovery of arm paresis to isolated motor function (BS 5 or 6) and time to achieve recovery. Recovered and nonrecovered patients were compared (Mann-Whitney, t tests, and chi(2)) on injury severity, initial level of paresis, age, time to rehabilitation admission, and pathology subtype. Time to recovery was compared for patients at different levels of initial paresis, ranges of LOC, and pathology subtypes (Mann-Whitney and Kruskal-Wallis tests).

RESULTS

Forty-four patients (17%) had moderate (BS 3 to 4) or severe (BS 1 to 2) paresis at rehabilitation admission. They were more severely injured than nonparetic patients based on longer LOC (p < .002) and PTA (p < .009). Thirty-six patients (82%) recovered by 6 months; 72% of these recovered by 2 months. If still paretic at 2 months, only 56% recovered. Mean recovery time was 6.9 weeks (SD, 6.1) from injury. Time to recovery was best predicted by initial level of paresis and injury severity (r2 = .48), but not age. Patients with diffuse injury tended towards a more protracted recovery (7.9 weeks, SD 6.5) than patients with focal injury (4.2 weeks, SD 3.9) (p = .08) and only those with diffuse injury showed further recovery after 3 months.

CONCLUSIONS

Arm paresis after TBI is relatively infrequent. Most patients recover by 2 months but later recovery is possible, especially in patients with primarily diffuse brain damage. Recovery is highly related to initial impairment, injury severity, and distribution of brain injury.

Comparison of older people and patients with frontal lesions: evidence from world list learning

We examined the hypothesis that changes in memory performance of older normal participants are due to frontal lobe dysfunction by comparing three groups of normal individuals (young, middle-aged, and older) with three groups of patients who had documented lesions in specific frontal regions: unilateral right, unilateral left, and bilateral. All participants were given 4 successive learning trials on each of 3 lists of words: unrelated, related but presented in a pseudo-random order, and related and presented in a blocked format. We found significant correspondences in performance between the older normal participants and the (younger) frontal damaged groups. The qualitative nature of recall performance, particularly as measured by indices of organizational control processes, was similar between older normals and patients with frontal damage, particularly those with right frontal damage, but different from that normally exhibited by patients with focal limbic/memory dysfunction. These results add to the evidence that at least some of the decline in older people in tasks which measure executive or supervisory abilities is due to frontal system dysfunction.

Specific semantic memory loss after hypoxic-ischemic injury

A patient is reported who suffered hypoxic-ischemic injury causing isolated and eventually partially reversible semantic memory loss. Despite normal MRI findings, single-photon emission CT demonstrated dysfunction in posterior cortical association areas. Semantic memory is the sum of categorical, perceptual, and conceptual knowledge. While not localized in a strict sense like visual fields, semantic memory is thought to be broadly organized in the posterior association cortices, with a particular focus in the inferior temporal regions. Evidence for this has come from patients with herpes simplex encephalitis, temporo-occipital infarctions, and dementias. This case confirms the importance of these cortical regions for semantic memory. The rapid recovery in this case, as opposed to the encephalitis or infarction cases, suggests an important role for preservation of white matter connections in the region for reconstitution of function.

Atypical cerebral dominance: predictions and tests of the right shift theory

Alexander and Annett (Brain and Language, in press) described new cases of atypical cerebral specialization, and suggested that these observations and others in the literature could be explained by the right shift (RS) theory. The theory generates specific predictions as to the prevalence of different patterns of cerebral dominance and their distribution among right-handers and left-handers. Predictions differ between strict and generous criteria of sinistrality, as between left writers and non-right-handers. Tests of the predictions against reports in the literature reveal good fits for most data. New studies will test the RS theory if their design permits examination of the present predictions.

Crossed aphasia and related anomalies of cerebral organization: case reports and a genetic hypothesis

Anomalous lateralization of cognitive functions is observed in a small percentage of right-handed patients with unilateral brain damage, either crossed aphasia (aphasia after right brain damage) or "crossed nonaphasia" (left brain damage without aphasia but with visuospatial and other deficits typical of right brain damage). No comprehensive theory of these anomalous cases has been proposed. Nine new right-handed cases (plus one left-handed case) were analyzed and the literature was reviewed. The dramatically anomalous organization of cognitive functions is best explained by random lateralization of all cognitive functions in a small subset of the population. The RS theory of cerebral dominance can account for this pattern of anomalies in right-handers and may account for the most common patterns of dominance observed in left-handers.

Recovery of memory and executive function following anterior communicating artery aneurysm rupture

We studied the recovery of memory and executive function in 10 patients following anterior communicating artery aneurysm (ACoA) rupture and repair. Patients were tested at 2 consecutive points in time following surgery (approximately at 2 and 3 months). At the first testing, the patients divided into 2 groups based on the severity of impairment on executive measures. Both groups had severe anterograde amnesia, but only patients with severe executive impairments had retrograde amnesia with a temporal gradient. At second testing, both groups had persistent severe anterograde amnesia. The dysexecutive group showed significant improvement in executive deficits and in retrograde amnesia, with attenuation of the temporal gradient. Patients with more severe executive impairments had more extensive bilateral frontal lesions than other patients. These results suggest that the cognitive profile following ACoA rupture changes with time. Time postonset following aneurysm rupture and lesion site are both critical for defining the neuropsychological profile, and determining the underlying cognitive mechanisms in this neurological disorder.

Incontinence after stroke in a rehabilitation setting: outcome associations and predictive factors

Urinary incontinence (UI) after stroke is common and associated with overall poor functional outcomes. There is controversy regarding which factors contribute to incontinence after stroke and which factors may be predictive of recovery of continence. This study investigated consecutive stroke admissions to an inpatient rehabilitation hospital and evaluated the impact of several pre-selected factors on the presence of UI and its recovery. We also studied the impact of UI on outcome in terms of functional abilities with the Functional Independence Measure (FIM) and in terms of disposition. UI on admission was associated with severe functional impairment with large infarctions and was probably caused by general severity rather than specific impairment of neuromicturition control. Patients with less impairment (admission FIM > 60) and small vessel strokes were likely to recover continence. UI on admission had a negative impact on outcome.

Verbal memory function in mild aphasia

Verbal material may be processed by semantic and phonologic systems. Damage to these language systems may also impair memory. We classified 16 mildly aphasic patients according to phonologic and lexicosemantic abilities, tested them on a variety of short- and long-term memory measures, and correlated behavioral deficits with lesion location. Aphasia impaired both short- and long-term memory. Phonologic impairment affected only digit span performance. Lexicosemantic deficits impaired self-organized encoding of word lists. Memory impairment was not associated with specific lesion locations. Persistent verbal-memory impairments accompanying even mild residual aphasia may be responsible for much of the difficulty mildly aphasic patients experience returning to vocational, academic, and social life. Co-occurrence of these deficits probably reflects their underlying dependence on similar processing systems.

Comparison of older people and patients with frontal lesions: evidence from world list learning

We examined the hypothesis that changes in memory performance of older normal participants are due to frontal lobe dysfunction by comparing three groups of normal individuals (young, middle-aged, and older) with three groups of patients who had documented lesions in specific frontal regions: unilateral right, unilateral left, and bilateral. All participants were given 4 successive learning trials on each of 3 lists of words: unrelated, related but presented in a pseudo-random order, and related and presented in a blocked format. We found significant correspondences in performance between the older normal participants and the (younger) frontal damaged groups. The qualitative nature of recall performance, particularly as measured by indices of organizational control processes, was similar between older normals and patients with frontal damage, particularly those with right frontal damage, but different from that normally exhibited by patients with focal limbic/memory dysfunction. These results add to the evidence that at least some of the decline in older people in tasks which measure executive or supervisory abilities is due to frontal system dysfunction.

Factors predictive of stroke outcome in a rehabilitation setting

Accurate outcome prediction following stroke is important for proper delivery of poststroke care. It has been difficult to determine specific factors that provide reliable and accurate predictions of outcome, particularly for patients with intermediate deficit severities. Age and severity of deficit have repeatedly been found to be most reliable, but only as rough estimates and for patients at either extreme of the disability spectrum. This paper reports a prospective study of consecutive rehabilitation admissions (N = 536) to determine the influence of preselected factors. Outcome was analyzed in terms of functional improvement and disposition. Patients younger than 55 years or with an admission Functional Independence Measure (FIM) greater than 80 almost universally went home. Admission FIMs less than 40 were associated with nearly certain nursing home discharge. The comprehensive FIM score was a stronger predictor of outcome than motor impairment in isolation. An admission FIM of 60 or greater was associated with a higher probability of functional improvement during rehabilitation. Small-vessel strokes had the best outcome. Intracerebral hemorrhages improved more than ischemic strokes but more slowly. Right hemisphere lesions did worse than left. Comorbidities influenced outcome only when several conditions accumulated. The absence of a committed caregiver at home increased the risk of nursing home discharge. Suggestions for rehabilitation triage are given.

Differential recovery from impairment to the phonological lexicon

Word production was examined in four aphasics diagnosed acutely with neologistic jargon and who displayed impairment to the lexical stage of phonological production (Kohn & Smith, 1993, 1994a). To investigate the major source of their nonword errors (i.e., neologisms, phonemic paraphasias), single word production was tested at three different times over the first 6 months postonset, with one subject receiving additional testing at 14 months postonset. Two subjects showed signs of recovery to the phonological output system with respect to: (1) improved word production scores, (2) increased frequency of phonemic paraphasias versus neologisms, and (3) increased production of target phonemes. These subjects also displayed above-chance production of target phonemes and no significant tendency to perseverate phonemes across picture-naming trials. It was argued that this pattern reflects a resolving disturbance in retrieving entries from the phonological lexicon. The other two subjects showed no improvement in word production. They also consistently produced target phonemes at chance levels and had a tendency to perseverate phonemes across picture-naming trials. This static pattern of performance was considered to reflect loss of information from the phonological lexicon. The neuroanatomical damage sustained by each case was consistent with these two recovery patterns.