Biomedical subjects

L J Buxbaum

Publications and source records attributed to L J Buxbaum.

12 recordsLinked to original sources

PubMed2004

Hemispatial neglect: Subtypes, neuroanatomy, and disability.

OBJECTIVE: To assess the relative frequency of occurrence of motor, perceptual, peripersonal, and personal neglect subtypes, the association of neglect and other related deficits (e.g., deficient nonlateralized attention, anosognosia), and the neuroanatomic substrates of neglect in patients with right hemisphere stroke in rehabilitation settings. METHODS: The authors assessed 166 rehabilitation inpatients and outpatients with right hemisphere stroke with measures of neglect and neglect subtypes, attention, motor and sensory function, functional disability, and family burden. Detailed lesion analyses were also performed. RESULTS: Neglect was present in 48% of right hemisphere stroke patients. Patients with neglect had more motor impairment, sensory dysfunction, visual extinction, basic (nonlateralized) attention deficit, and anosognosia than did patients without neglect. Personal neglect occurred in 1% and peripersonal neglect in 27%, motor neglect in 17%, and perceptual neglect in 21%. Neglect severity predicted scores on the Functional Independence Measure and Family Burden Questionnaire more accurately than did number of lesioned regions. CONCLUSIONS: The neglect syndrome per se, rather than overall stroke severity, predicts poor outcome in right hemisphere stroke. Dissociations between tasks assessing neglect subtypes support the existence of these subtypes. Finally, neglect results from lesions at various loci within a distributed system mediating several aspects of attention and spatiomotor performance.

Activities of Daily Living↗

PubMed2004

Patterns of spontaneous recovery of neglect and associated disorders in acute right brain-damaged patients.

OBJECTIVES: The evolutionary pattern of spontaneous recovery from acute neglect was studied by assessing cognitive deficits and motor impairments. Detailed lesion reconstruction was also performed to correlate the presence of and recovery from neglect to neural substrates. METHODS: A consecutive series of right brain-damaged (RBD) patients with and without neglect underwent weekly tests in the acute phase of the illness. The battery assessed neglect deficits, neglect-related deficits, and motor impairment. Age-matched normal subjects were also investigated to ascertain the presence of non lateralised attentional deficits. Some neglect patients were also available for later investigation during the chronic phase of their illness. RESULTS: Partial recovery of neglect deficits was observed at the end of the acute period and during the chronic phase. Spatial attention was impaired in acute neglect patients, while non spatial attentional deficits were present in RBD patients with and without acute neglect. A strong association was found between acute neglect and fronto-parietal lesions. Similar lesions were associated with neglect persistence. In the chronic stage, neglect recovery was paralleled by improved motor control of the contralesional upper limb, thus emphasising that neglect is a negative prognostic factor in motor functional recovery. CONCLUSIONS: These findings show that spatial attention deficits partially improve during the acute phase of the disease in less than half the patients investigated. There was an improvement in left visuospatial neglect at a later, chronic stage of the disease, but this recovery was not complete.

Acute Disease↗

PubMed2001

Hand-centered attentional and motor asymmetries in unilateral neglect.

On several accounts of "selection for action", acting on a target object among distractors requires that irrelevant inputs and responses to these inputs are inhibited, and relevant inputs and responses selected. In unilateral neglect associated with right-hemisphere lesions, selection processes may be biased toward stimuli on the right, as right is usually defined by head and body hemispace. In normal subjects performing reaching-to-target tasks, selection may be "hand-centered" (Tipper S., Lortie C., Baylis G.C., Journal of Experimental Psychology: Human Perception and Performance 18(4) (1992) 891-905) in that distractor stimuli close to the hand compete strongly with the target for the control of action, causing greater interference than distractors far from the hand. We reasoned that in the context of a reaching task, a left-right asymmetry in unilateral neglect may be defined with respect to the position of the hand. This predicts that target and distractor stimuli to the left of hand (i.e. requiring leftward movements for contact) should compete less strongly for the control of action than stimuli to the right of the hand. We tested this hypothesis by asking eight patients with unilateral neglect (and 12 healthy controls) to reach to central targets presented alone and with surrounding distractors from left or right start positions. Patients with neglect, but not controls, were slower to initiate reaches from right start as compared to left start positions. In this context, patients showed interference from distractors to the right of the hand and facilitation from distractors to the left of the hand. This indicates that a left-right selection asymmetry in neglect may be hand-centered. These data can be explained on a model of damage to the portion of a distributed neuronal population coding movement vectors to stimuli in relatively leftward locations.

Adult↗

PubMed2001

Ideomotor apraxia: a call to action.

Although ideomotor apraxia (IM) has been a topic of investigation since the early 20th century, progress in studying the disorder has been hindered by important (and sometimes unarticulated) differences in the underlying theoretical models of various investigative groups. As a result, it is difficult to draw conclusions about the expected performance of IM patients on various tests of praxis (e.g. pantomime, single object use, gesture imitation, and naturalistic action); the relationship of IM to ideational apraxia (IA); the degree to which specific error types are diagnostic of one or the other disorder; the relationship of semantic knowledge to gesture representations; and the role of spatiomotor systems external to the stored gesture representation system. Here an updated model of IM is presented, informed by recent physiological and functional neuroimaging literature, as a step towards resolving some of these concerns. The model is intended to lay the groundwork for future investigations of specific performance patterns in different subtypes of IM.

Apraxia, Ideomotor↗

PubMed2000

The role of the dynamic body schema in praxis: evidence from primary progressive apraxia.

On an influential model of limb praxis, ideomotor apraxia results from damage to stored gesture representations or disconnection of representations from sensory input or motor output (Heilman & Gonzalez Rothi, 1993; Gonzalez Rothi et al., 1991). We report data from a patient with progressive ideomotor limb apraxia which cannot be readily accommodated by this model. The patient, BG, is profoundly impaired in gesturing to command, to sight of object, and to imitation, but gestures nearly normally with tool in hand and recognizes gestures relatively well. In addition, performance is profoundly impaired on imitation of meaningless gestures and on tasks requiring spatiomotor transformations of body-position information. We provide evidence that BG's apraxia is largely attributable to impairments external to the stored gesture system in procedures coding the dynamic positions of the body parts of self and others; that is, the body schema. We propose a model of a dynamic, interactive praxis system subserved by posterior parietal cortex in which stored representational elements, when present, provide "top-down" support to spatiomotor procedures computed on-line. In addition to accounting for BG's performance, this model accommodates a common pattern of ideomotor apraxia more readily than competing accounts.

Aged↗

PubMed1999

Impaired face and word recognition without object agnosia.

A leading account of high-level visual recognition proposes that the recognition of faces, objects, and words is mediated by two processing capacities. Words are assumed to require the capacity to represent numerous parts, whereas faces are processed wholistically. and hence require the representation of complex units. Object recognition requires the capacity to represent both numerous and complex parts. As object recognition depends upon the same processing capacities underlying face and word recognition, this account predicts that patients with severe alexia and prosopagnosia should be deficient in tests of object recognition. We report a patient who is unable to recognize words or faces, yet performs relatively well on tests of object recognition. The two-capacity theory cannot accommodate this pattern of performance without additional assumptions.

Agnosia↗

PubMed1999

Naturalistic action production following right hemisphere stroke.

An unselected group of right hemisphere, semi-acute stroke patients (n = 30) was run on a laboratory test of naturalistic action production and was found to commit errors of action at a higher rate than what was previously reported for recovering head injury patients [Schwartz et al., Naturalistic action impairment in closed head injury. Neuropsychology, 1997, 8, 59-72]. There were strong similarities in how these two patient groups responded to variations in task demands and in the pattern of errors they produced. Hemispatial biases were evident in the errors of right hemisphere patients with neglect but not those without neglect; and neglect patients also many errors that were unrelated to the spatial layout. We argue that a non-specific resource limitation--which might translate as reduced arousal or effort--is central to the breakdown of naturalistic action production after brain damage, and right hemisphere patients are especially vulnerable to this resource limitation and its behavioral consequences.

Adult↗

PubMed1998

Naturalistic action impairment in closed head injury.

The authors sought to determine whether errors of action committed by patients with closed head injury (CHI) would conform to predictions derived from frontal lobe theories. In Study 1, 30 CHI patients and 18 normal controls performed routine activities, such as wrapping a present, under conditions of graded complexity. CHI patients committed more errors even on the simplest condition; but, except for a higher proportion of omitted actions, their error profile was very similar to that of controls. Study 2 involved a subset of patients whose performance in Study 1 was within normal limits. When these high functioning patients were asked to perform the routine tasks under still more taxing conditions, they, too, committed errors in excess of the control group. Accounts based on frontal mechanisms have a difficult time explaining the overall pattern of findings. An alternative based on limited-capacity resources is suggested.

Activities of Daily Living↗

PubMed1996

Deep dyslexic phenomena in a letter-by-letter reader.

Numerous accounts of pure alexia have suggested that prelexical impairment precludes rapid access to orthographic information in patients with the disorder. We report a patient with features of both pure and partially recovered deep dyslexia in whom we demonstrate prelexical deficits in maintaining a reliable abstract representation of the right side of letter arrays, as well as in modulating a "spotlight" of visual attention. These deficits, we suggest, encourage the patients's use of a letter-by-letter reading strategy; despite them, however, he demonstrates rapid, accurate reading of some, but not all classes of words. Furthermore, the patient's reading is influenced by both prelexical and lexical-semantic factors such that speed and accuracy are optimal for high imagiability nouns of few letters. Finally, the patient accurately names orally spelled words of all classes. Taken together, these data are consistent with the hypothesis that rapid reading may be enabled by lexical-semantic support from a right hemisphere-mediated processing system which recognizes words as whole, thereby mitigating the effect of the prelexical deficits.

Brain Ischemia↗

PubMed1996

Mental rotation may underlie apparent object-based neglect.

Previous investigations have suggested that object-based neglect may reflect an impairment in attentional allocation that occurs relative to the intrinsic left and right of objects. We report a patient with apparent "object-based" neglect of 90 degrees rotated stimuli for whom the pattern of neglect was a function of task strategy. When the patient was instructed to visualize the rotated stimuli as if they were upright, i.e. mentally rotate them, he showed apparent "object-based" neglect to the left of the principal axes of the stimuli. In contrast, when instructed to refrain from mental rotation, neglect was apparent only with respect to his left, but not the left of the stimuli. Thus, the apparent "object-based" neglect of this patient may be attributed to a process of mental rotation of objects to upright, and subsequent neglect in viewer-centered or environment-centered coordinates. These data suggest a mechanism whereby object-based and viewer/environment-centered reference frames may be aligned, thereby causing viewer/environment-centered neglect to appear as if object-based.

Aged↗

PubMed1994

Neglect of chimeric figures: two halves are better than a whole.

From a group of 22 patients with neglect, we identified five patients who neglected the left sides of "chimeric" figures composed of the conjoined right and left halves of drawings of two different objects; these subjects reported the left half-drawing significantly more accurately when a gap was introduced between the chimeric halves. The improvement in the "gap" condition cannot be attributed to the subjects' recognition that the right-sided stimuli were incomplete, as when whole figures were presented on the right along with left-sided half figures, the enhancement in reporting accuracy was maintained. For at least one patient, sufficient information was available about the neglected stimuli to support accurate recognition in a forced-choice task with foils visually similar to the targets. On the basis of these and other data, we propose that for these patients with neglect, visual processing systems subserving the registration of discrete object markers in a spatial map are at least relatively intact, but that there is an impairment in the allocation of attention to the left sides of these markers.

Aged↗

PubMed1993

Hemispatial factors in mirror writing.

The effect of the hemispace in which writing was performed was assessed in two left hemisphere stroke patients who demonstrated left-handed mirror writing. Both patients produced significantly more mirrored words when writing in right, as compared to left (body) hemispace. We suggest that writing in the right hemispace activates the left hemisphere. Further, we propose that mirror writing in the right hemispace is attributable to activation of the damaged left hemisphere spatial system, which fails to assist in the translation of right hand motor programs into those appropriate to the left hand. Writing in left hemispace, in contrast, activates the intact right hemisphere based spatial system which guides the execution or monitoring of motor productions in left hemispace. The result is writing which remains directionally correct when the left hand is used in left hemispace.

Agraphia↗