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Biomedical subjects

R T Watson

Publications and source records attributed to R T Watson.

At least 19 recordsLinked to original sources
PubMed1994

Posterior neocortical systems subserving awareness and neglect. Neglect associated with superior temporal sulcus but not area 7 lesions.

OBJECTIVE: In humans and monkeys, the intraparietal sulcus separates the superior parietal lobule from the inferior parietal lobule (IPL). Whereas in humans Brodmann's area 7 is above this sulcus, in monkeys it is below and therefore part of the IPL. In humans, the IPL consists of Brodmann's areas 39 and 40. Some investigators contend that the monkey homologue of the human IPL (areas 39 and 40) is the monkey's IPL (area 7). Others contend that it is, at least in part, in the monkey's superior temporal sulcus (STS). In humans, IPL lesions induce neglect. Although IPL lesions in monkeys also have been reported to induce neglect, the STS was involved in these lesions. We sought to learn which of these two areas, when ablated, produces neglect. DESIGN: Study of five adult stump-tailed macaque monkeys by making five isolated STS and six IPL lesions. RESULTS: Inferior parietal lobule lesions were associated with misreaching but not with unilateral neglect. Neglect was observed in association with five of the six STS lesions. CONCLUSIONS: With regard to neglect, STS may be the monkey homologue of the human IPL. Animals with STS lesions and humans with IPL lesions may manifest unilateral neglect because these areas are necessary for normal awareness of external stimuli. This awareness may result from the integration of the areas important in stimulus localization (the "where is it?" system) and stimulus identification (the "what is it?" system), as well as the areas important in defining the biologic importance of stimuli, such as the frontal lobes and limbic areas.

Animals↗
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

Apraxia due to a pathologically documented thalamic infarction.

We report a pathologically documented case of infarction of the dominant thalamus with extensive involvement of the ventral lateral, ventral posterolateral, and lateral posterior nuclei and some involvement of the pulvinar. This patient exhibited linguistic impairment with features fairly typical for thalamic lesions. He also demonstrated a severe ideomotor apraxia. The preservation of repetition, syntax, and implicit memory despite severe naming deficits in patients with thalamic lesions suggests the possibility that thalamic involvement in cognitive function involves processes underlying declarative as opposed to nondeclarative (eg, implicit or procedural) memory. The occurrence of apraxia with thalamic lesions may be consistent with this hypothesis if it is accepted that only actual tool use approaches a pure skill that involves only nondeclarative memory, while other aspects of praxis implicate declarative memories.

Aged↗
PubMed1990

Frontal hypermetabolism and thalamic hypometabolism in a patient with abnormal orienting and retrosplenial amnesia.

A patient with verbal amnesia and a propensity to direct his attention to the right following a retrosplenial area lesion was studied with positron emission tomography using [F-18] fluorodeoxyglucose. These studies showed that the left thalamus was hypometabolic, and the anterior 2/3 of the left hemisphere was hypermetabolic when compared with the right. There were no significant differences seen in the medial temporal lobes. Based on this study, it is posited that interruption of hippocampal input into the anterior thalamus was responsible for the amnesia, and the left frontal hyperactivity was associated with the propensity to attend contralaterally.

Adult↗
PubMed1989

Loss of spontaneous blinking in a patient with Balint's syndrome.

A patient with Balint's syndrome caused by bilateral parieto-occipital lesions lost spontaneous blinking, suggesting that humans, like nonhuman primates, have parietal lobe neurons that are important for blinking. Although the functions of spontaneous blinking are not known, they may help initiate some saccades and, like saccades, be involved in the cancellation of thalamic inhibitory postsynaptic potentials, thereby facilitating processing of new foveal targets. Spontaneous blinking may also facilitate sensory relay during sustained attention and, therefore, help prevent fading of a retinal image.

Adult↗
PubMed1989

Bibrachial palsy due to paraneoplastic encephalomyelitis.

Bibrachial palsy is a distinctly unusual pattern of muscular weakness. We have described a woman who had a slowly progressive clinical course, with profound bibrachial palsy and neurogenic respiratory failure, but neurologically normal lower extremities. Autopsy revealed encephalomyelitis and a small previously undetected oat cell carcinoma with inflammatory infiltration. The pathologic features are consistent with an autoimmune process.

Brachial Plexus↗
PubMed1988

Changes in sensory inattention, directional motor neglect and "release" of the fixation reflex following a unilateral frontal lesion: a case report.

We recorded eye movements to and away from visual stimuli from a patient with left-sided neglect following a right frontal infarct in order to determine (a) whether and to what extent his neglect was due to sensory inattention and directional motor neglect and (b) whether he had difficulty suppressing inappropriate eye movements to visual stimuli ("release" of visual grasp) as his sensory inattention declined. In the first testing session, conducted 5 days following his stroke, he often failed to move his eyes when a stimulus on the left required a rightward eye movement, but he consistently moved his eyes to a stimulus on the right. Thus, he showed contralateral but not ipsilateral sensory inattention. Initially, he also was impaired in making leftward eye movements when right stimuli were presented. Thus, he also showed a directional motor neglect. In subsequent tests, his left-sided sensory inattention as defined above decreased, and was no longer present three weeks following his stroke, nor in a follow-up test conducted almost 6 months following this stroke. In contrast, his directional motor neglect, as defined above, was still present in the follow-up test. As his left-sided sensory inattention declined, his tendency to move his eyes incorrectly to stimuli on the left side (the side contralateral to his lesion) when these stimuli required eye movements to the right became stronger ("release" of visual grasp); he continued to show this strong tendency in the test conducted almost 6 months following his stroke.

Attention↗
PubMed1988

Pupil-sparing oculomotor palsy from midbrain hemorrhage.

Pupil-sparing oculomotor nerve palsy generally results from extraaxial lesions, but it has also been seen with intraaxial infarcts and tumors. This report of a midbrain hemorrhage in a 64-year-old man supports the idea of selective interference with widely separated oculomotor nerve fascicles as the mechanism for intraaxial pupil-sparing oculomotor nerve palsies.

Cerebral Hemorrhage↗
PubMed1987

Response time in monkeys with unilateral neglect.

Four monkeys were trained to open a door with either the right or left hand in response to a tactile stimulus to either leg. After unilateral frontal arcuate ablation inducing unilateral neglect, the response time on this task increased most when the monkey responded with the hand contralateral to the lesion, but also increased when the monkey used the hand ipsilateral to the lesion. The side of stimulation had no effect on response time. Control (anterior superior temporal) lesions did not cause neglect and only affected response time slightly in one monkey (using the limb contralateral to the lesion). We conclude that response time is increased in animals with unilateral neglect and that the increase results from a defect in intention to act (motor neglect) rather than from sensory neglect.

Animals↗
PubMed1987

Efferent connections of the rostral portion of medial agranular cortex in rats.

This study of the rostral part of medial agranular cortex (AGm) was undertaken with two principal aims in mind. First, to delineate the efferent connections of AGm and compare these with the pattern of afferents defined by us in a previous study. Second, to provide a firmer basis for anatomical and functional comparisons with cortical regions in monkeys. Autoradiographic, horseradish peroxidase, and fiber degeneration techniques were used. Rostral AGm has a variety of corticocortical connections--with lateral agranular motor cortex (AGl); visual, auditory, and somatic sensory regions; and limbic/paralimbic areas including orbital, insular, perirhinal, entorhinal, retrosplenial and presubicular fields. The projections to orbital, perirhinal and entorhinal cortices are bilateral. Thalamic projections of rostral AGm are concentrated in the ventral lateral, central lateral, paracentral, mediodorsal and ventromedial nuclei. Moderate terminal fields are consistently seen in the reticular, anteromedial, central medial, gelatinosus, parafascicular, and posterior nuclei. More caudal projections reach the central gray, superior colliculus and pontine gray. The efferents of the adjacent AGl were also examined. Although many of these overlapped those of rostral AGm, there were no efferents to visual or auditory cortex and limbic/paralimbic projections were reduced. Thalamic projections were more focused in the ventral lateral and posterior nuclei and there were no terminal fields in the central gray or superior colliculus. Based on its afferent and efferent connections, role in contralateral neglect, and the results of microstimulation studies, rostral AGm can be viewed as a multimodal association area with strong ties to the motor system. On these structural and functional grounds, rostral AGm bears certain striking resemblances to the frontal eye field, supplementary motor, and arcuate premotor areas of monkey cortex.

Animals↗
PubMed1987

Transitive movements in a deafferented man.

It has not been determined if the performance of transitive movement requires sensory feedback from the limb to the brain. We tested a deafferented patient's ability to pantomime, imitate, and use actual objects in both eyes open and eyes closed conditions. Although his performance deteriorated when his eyes were closed, the major error made by this patient was the inability to correctly orient the instrument (or pretended instrument) toward the object of the instrument's action.

Adult↗
PubMed1987

Retrosplenial amnesia.

A 39-year-old man developed retrograde and anterograde amnesia following haemorrhage from an arteriovenous malformation situated near the splenium of the corpus callosum. MRI studies demonstrated damage to the splenium, and to a region containing the retrosplenial cortex and the cingulate bundle. The fornix was anterior and inferior to the site of maximal damage, but may have been involved; the stria terminalis was probably spared. Structures known to be important in memory but spared by the lesion included the hippocampus, thalamus, and basal forebrain. The retrosplenial cortex receives input from the subiculum and projects to the anterior thalamus, thus providing an alternative route between hippocampus and thalamus. Perhaps more importantly, medial temporal structures involved in memory receive anterior thalamic input directly via the cingulate bundle and indirectly through a relay in the retrosplenial cortex. We suggest that this thalamocortical portion of Papez' circuit may be important in memory, and that lesions of the cingulum and retrosplenial cortex may cause amnesia by disrupting this pathway.

Adult↗
PubMed1987

Hemispace-visual field interactions in visual extinction.

Visual extinction was studied in a patient with neglect from a right hemispheric lesion. Extinction occurred during double simultaneous stimulation within the same visual hemi-field (VHF). This finding suggests that interhemispheric rivalry is not a critical factor. During double simultaneous stimulation within the same VHF as well as with stimuli in different VHFs, the severity of extinction was determined by both the retinotopic and the hemi-spatial position of the extinguished stimulus. The location of the other stimulus, however, did not seem relevant. It is proposed that damage to a corticolimbic-reticular system reduces attentional capacity and that extinction during double simultaneous stimulation in the visual modality reflects an inability to distribute the limited attentional resources equally to two different locations. The severity of extinction is a measure of an unequal distribution of attention along a gradient within visual space.

Attention↗
PubMed1987

Dopamine agonist therapy for neglect in humans.

Lesions of ascending dopaminergic pathways induce neglect in animals. Apomorphine, a dopamine receptor agonist, decreases the magnitude of neglect in rats with cortical lesions. We treated two patients with 15 mg of bromocriptine daily for 3 to 4 weeks, one with chronic (longer than 6 months) and one with relatively more acute disabling neglect. Tests for neglect that significantly improved on therapy and worsened after its withdrawal included line, letter, and geometric figure cancellation tasks. Neither patient noted any untoward effects. Based on this open trial of dopamine agonist therapy in humans with neglect, larger controlled studies may be warranted.

Adult↗
PubMed1986

Apraxia and the supplementary motor area.

Anatomical, electrophysiological, and cerebral blood flow studies suggest that the supplementary motor area (SMA) may be important for programming certain skilled motor acts of the limbs. However, to our knowledge, abnormalities of complex distal motor behavior following SMA lesions have not been reported. We have studied two patients with left mesial hemisphere infarctions that included the SMA. These patients had bilateral ideomotor apraxia for transitive limb movements without buccofacial apraxia. The observations suggest that the types of skilled motor acts programmed by the left SMA are learned transitive limb movements.

Aged↗
PubMed1986

Apomorphine has a therapeutic effect on neglect produced by unilateral dorsomedial prefrontal cortex lesions in rats.

Neglect is a disorder in which the response to stimulation is diminished or absent on the side of the body contralateral to the lesion in the absence of an elemental sensory or motor defect. Most cases of neglect in humans are induced by cortical damage, but there have been no investigations of the pharmacologic basis of neglect induced by cortical damage. We examined the role of the dopamine system in polymodal neglect caused by a unilateral lesion of the medial precentral prefrontal cortex of the rat. A dose-response examination of the effect of apomorphine on neglect revealed that apomorphine, at 0.5 mg/kg, the highest dose examined, significantly improved the orientation scores of subjects in all modalities tested and significantly decreased the total number of allesthetic responses. The therapeutic effect of apomorphine was mediated by dopamine receptors as the therapeutic effect of apomorphine was blocked by prior administration of spiroperidol. These results demonstrate the important role of disruption of dopamine mechanisms in neglect induced by a lesion of medial precentral cortex.

Animals↗
PubMed1986

Apraxia after a superior parietal lesion.

We studied a patient who had unilateral (left) limb apraxia associated with a lesion of her right superior (Brodmann areas 5 and 7) and inferior parietal lobes. In monkeys areas 5 and 7 contain "hand-manipulation neurons" that are thought to be important in proprioceptive guidance. Therefore, we tested our patient with her eyes open and closed. Her left hand performance with pantonime, imitation, and use of actual objects dramatically deteriorated in the absence of visual guidance. In addition, although the patient did not have optic ataxia and had normal proprioception, she had difficulty using her left forelimb in tasks that require transcoding from a visual to a somatesthetic spatial coordinate system. We propose that each superior parietal lobe is not only responsible for transcoding from a visual-spatial code into a somatesthetic-spatial code but is also critical for transcoding spatial-temporal representations of skilled movement into a somatesthetic-spatial code.

Adult↗