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Biomedical subjects

K M Heilman

Publications and source records attributed to K M Heilman.

At least 163 records · Page 9Linked to original sources
PubMed1994

Visual field influence on radial line bisection.

An attentional bias toward far peripersonal space has been proposed as the mechanism underlying inaccurate bisection of lines oriented radially in the sagittal plane. The position of stimuli in the visual scene has also been proposed as an important determinant of visual attention. This study was designed to evaluate the relative contributions of spatial and visual field factors in bisection of radial lines. The usual linkage of distant space and upper visual field was dissociated by assessing line bisection above eye level. Ten normal subjects bisected twelve 20-30-cm lines 35 cm above eye level and the identical stimuli 35 cm below the eyes. The previous findings of misbisection of radial lines distant to true center was replicated when stimuli were presented below eye level. Lines above eye level were misbisected significantly closer to the subjects. The findings suggest that visual field position influences the allocation of attention in the radial axis of space.

Adult↗
PubMed1994

Lack of error awareness in an aphasic patient with relatively preserved auditory comprehension.

The neuropsychological mechanisms underlying unawareness of speech/language deficits are unknown, but four possibilities have been suggested: impaired lexical-semantic representations associated with impaired speech comprehension, a failure of feedback, reduced attentional capacity, and psychological denial. We studied a patient who was unaware of his jargon aphasia despite only a mild auditory comprehension disturbance. Delaying auditory feedback altered his speech patterns. He recognized more of his errors in a recording of his voice than he did while speaking. He also recognized more errors in a recording of the examiner making errors than he did when listening to the recordings of his own speech. Based on these results, we suggest that none of the proposed mechanisms can exclusively account for this man's performance and that each may contribute to his failure to detect and correct errors in speech production.

Aged↗
PubMed1994

Contributions of the parietal and frontal lobes to sustained attention and habituation.

The parietal cortex may be important in sustaining attention toward visual stimuli in peripheral space whereas the frontal cortex may mediate selective attention through habituation to peripheral stimuli. To test this hypothesis, patients with focal lesions of either the parietal or frontal cortex or both and normal controls were studied using a paradigm known as Troxler fading. Accordingly, if one fixates on a centrally located stimulus and attends to a stationary stimulus in peripheral vision, the peripheral stimulus quickly fades from awareness (i.e. Troxler fading: Troxler [Verschwinden, unseres, Opthal, Vol. 2, pp. 51-53. Fromann, Jena, 1804]). Movement of the peripheral stimulus on the retina normally prevents Troxler fading. Results indicated that patients with parietal lesions not only reported accelerated Troxler fading but also reported fading of moving peripheral stimuli contralateral to their brain lesion. In contrast, patients with frontal lesions rarely reported Troxler fading. In one patient with a left parietal and a right frontal lobe lesion fading was hemi-spatially dissociated, being accelerated in right hemispace but absent in left hemispace. These observations suggest that the parietal and frontal cortices play complementary roles in attentional processing.

Aged↗
PubMed1994

Planum temporale asymmetry and language dominance.

Language is lateralized to the left hemisphere in most individuals, and leftward asymmetry of the planum temporale has been reported in postmortem and imaging studies. In this study we measured the planum temporale on magnetic resonance imaging (MR) scans of patients (11 right-handers, 1 non-right-hander) who had selective hemispheric anesthesia or Wada testing performed for language lateralization. All subjects who had language lateralized to the left hemisphere (11 right-handers) had a leftward asymmetry of the planum temporale. One subject who had language lateralized to the right hemisphere (non-right-hander) had a strong rightward asymmetry of the planum temporale. These data suggest that planum temporale asymmetries determined by MR are associated with language dominance and may predict language laterality.

Adolescent↗
PubMed1994

The neglected page.

Normal subjects bisect vertical lines above the true midpoint. We posited that the portion of the page farthest from the line or the page's geometric center, though not the focus of attention, would still engage attention. Therefore, subjects should make bisection errors in the direction of the distant portion or geometric center. We expected the greatest superior bisection errors to be made when lines were placed at the bottom of the page and the smallest errors to be made when the lines were placed at the top of the page. Ten young, normal subjects bisected vertical lines placed in 1 of 3 positions on a page (top, center, bottom) with the page located in 1 of 3 spatial locations (superior, middle, inferior). The results of our study were consistent with our predictions. Thus, although the page on which a line is bisected is often ignored, it is not neglected.

Adult↗
PubMed1994

A comparison of the influences of body and environment centred reference frames on neglect.

Extrapersonal space can be defined by coordinate systems, or frames of reference, that are centred on the body (viewer) or on the environment. Although these frames are identical in the upright position, when the body is placed in positions orthogonal to gravity, the frames may be dissociable. We compared the influences of environmental and body-centred frames on line bisection in two patients with neglect who, when upright, neglected opposite dimensions of space. Through certain combinations of line placement and body orientation, the body and environmental frames were brought into opposition, and each frame predicted line bisection errors in an opposite direction. When the patients were positioned so that predictions of the two frames contrasted, both bisected lines as predicted by the environmental rather than the body-centred frame.

Aged↗
PubMed1994

Spatial planning deficits in limb apraxia.

Geschwind (1975) proposed a disconnection model in which an apraxic subject is unable to carry out movements to command because the left hemisphere that comprehended the verbal command is disconnected from the right premotor and motor areas which controls the left hand. An alternate model, however, proposes that apraxia results from destruction of spatiotemporal representations of learned movement stored in the left hemisphere (Heilman, 1979). The disconnection hypothesis would predict that apraxic subjects should be able to correctly imitate gestures and correctly use actual tools since these tasks do not require language. The movement representation model predicts that imitation and actual tool use would also be impaired. Motion analyses were performed on the trajectories of repetitive 'slicing' gestures made in a series of conditions in which contextual cues were introduced in a graded fashion. Four cue conditions were presented: no cues (verbal command), object present, tool present and both object and tool present. Positions of the hand, wrist, elbow, and shoulder were digitized from neighbouring views, reconstructed in three dimensions and analysed with respect to specific spatiotemporal features of the trajectories. Three subjects with limb apraxia, who had lesions that included left parietal cortex, and four neurologically intact subjects participated. The apraxic subjects showed disturbances in planning the movement of the hand in space across the cue conditions. For example, they showed deficits in the plane of motion, the shape of the trajectory and in the coupling of hand speed and trajectory shape even when given full contextual cues. These data support the hypothesis that apraxia can result from the destruction of spatiotemporal representations of learned movement, rather than from a disconnection between the receptive language areas in the left hemisphere and the contralateral motor cortices.

Aged↗
PubMed1994

Conduction apraxia.

A left hemisphere damaged patient with ideomotor apraxia is described, whose performance on pantomime to verbal command was superior to pantomime imitation. His reception of these same gestures (gesture naming) was spared. This syndrome has been named conduction apraxia. To account for this selective impaired performance on gesture imitation, a separation of the representations for gesture production and reception is proposed and a non-lexical gesture processing route for gesture imitation is suggested.

Aged↗
PubMed1994

Proximal intentional neglect: a case study.

Although neglect has been demonstrated in the horizontal, vertical, and radial planes of space and has been attributed to sensory-attentional, motor-intentional, and representational deficits, motor intentional neglect in the radial plane has not been previously described. A patient who had a right parietal infarct was tested with a modified cancellation task that uses a fixed window, thereby controlling attentional demands and allowing one to dissociate between intentional and representational neglect. This patient showed proximal (radial) intentional neglect (a failure to move towards or in proximal space). Unlike controls whose search times decreased with increasing window size, our patient showed no change in search time as a function of window size. This pattern of behaviour suggests that the patient's search strategy does not incorporate factors such as the relation between a fixed target space and a variably sized aperture, but rather was based on the allocation of a certain amount of resources for a fixed period of time after which, regardless of performance, the patient would stop searching.

Aged↗
PubMed1994

Anosognosia for hemiplegia: an electrophysiologic investigation of the feed-forward hypothesis.

The cause of anosognosia for hemiplegia (AHP) remains unclear. Weakness is detected when there is a mismatch between the expectancy of movement and the sensory perception of movement. The feed-forward hypothesis of AHP posits that there is a failure of detection because there is a loss of motor intention and expectancy of movement. We tested motor intention by measuring the activation of proximal muscles (pectoralis majoris) while subjects squeezed a dynamometer with each hand. We tested a group of normal controls, a group of patients with hemiparesis, a patient with neglect, a patient with resolved AHP, and a patient with persistent AHP. The patient with AHP did not contract either of his pectoralis muscles when asked to squeeze with his contralesional, paretic hand, yet he contracted both of them when squeezing the dynamometer with his ipsilesional hand. Normal controls, hemiparetic controls, and the patient with hemispatial neglect contracted both pectorales when asked to squeeze with each hand. The pattern of activation seen in the patients with persistent AHP and resolved AHP demonstrates a loss of motor intention and lends support to the feed-forward hypothesis of AHP.

Agnosia↗
PubMed1994

Motor neglect associated with a discrete parietal lesion.

The syndrome of motor neglect may follow brain lesions affecting frontal, subcortical, and parietal structures. However, pure motor neglect has not been previously associated with a lesion confined to the parietal lobe. We observed a 79-year-old right-handed man with right-sided limb akinesia and motor neglect without concomitant sensory or visuospatial neglect. MRI showed a left posterior parietal infarct sparing the primary sensorimotor cortex. Transcranial magnetic stimulation showed comparable thresholds for electromyographic activation of the muscles of the right and left arm and normal central motor conduction times, indicating functional integrity of the motor cortex. This case demonstrates that a discrete parietal lesion can produce a pure intentional disorder, independent of sensory or visuospatial neglect.

Aged↗
PubMed1993

Right hemisphere facial expressivity during natural conversation.

Most studies of facial expressivity in patients with focal brain lesions have examined the ability to produce emotional expression in laboratory settings using various experimental paradigms. In this study, we compared facial expressivity in right hemisphere damaged patients (RHD), left hemisphere damaged patients (LHD), and normal controls (NHD) during videotaped semistructured interviews with the patient and spouse in their home. Three research assistants rated 120 10-sec segments of videotape per patient on a 7-point expressivity scale. We found that RHD patients showed reduced facial expressivity in comparison to both LHD and NHD subjects during spontaneous conversation. In particular, RHD patients demonstrated significantly less smiling and laughter than LHD patients and normal controls. These findings were not a general feature of communicative competence in RHD patients as discourse production equaled that of normal controls. These results support the hypothesis that the right hemisphere mediates facial expressivity during spontaneous social interaction.

Aged↗
PubMed1993

Hemispheric specialization for handwriting in right handers.

Hand preference may be related to either lateralized language, movement representations, or both. Anatomic and behavioral studies have revealed that whereas each hemisphere has motor control of the contralateral distal and proximal limb movements, this same hemisphere's control over the ipsilateral limb is limited to proximal movements. This differential proximal-versus-distal organization may have functional implications such that when right handers write with their left hand they must be use more proximal musculature than when they write with their right hand. If hand preference is related to lateralized movement representations, right handers may also use more proximal than distal movements when drawing with their left than with their right hand. If one uses distal musculature to write or draw, the elbow travels through space less than if one uses proximal musculature. We studied 12 right handers by having them write and draw with their right and left hands and measured the spatial amplitude of their elbow movements. We found that when writing or drawing, right handers moved their left elbow more than their right. These results suggest that it is the lateralized movement representations that may be primarily responsible for writing hand preference.

Adolescent↗
PubMed1993

Memory, mood and measurement in hypothyroidism.

A 63-year-old female exhibited primary hypothyroidism, both upon clinical examination and laboratory tests. A full neuropsychological exam and repeated, multiple measures of affect, memory, concentration, and problem solving were used to establish baselines prior to treatment and to assess change during the first 7 months of thyroid hormone replacement therapy. Additionally, thyroid hormone and metabolites T3, T4, TSH, and T3 (resin uptake) were regularly assessed. Results indicated that establishing stable baselines before treatment, long-term repeated assessments during treatment, and the use of control subjects are crucial to understanding the neuropsychological changes associated with hypothyroidism. Certain measures of depression, anxiety, attention, and concentration changed from severely impaired to normal levels following an explanation of the diagnosis but before actual treatment. Baseline memory functions were impaired before treatment and remained impaired relative to normals during replacement therapy in spite of improvement with repeated testing. However, replacement therapy may have arrested the progression of memory deterioration as no further decline was evident at a 7-month follow-up. Our data suggest that the memory changes associated with primary hypothyroidism may not be reversed by thyroid hormone replacement therapy.

Affect↗