Axial motor disturbances after hypoxic lesions of the globus pallidus

Implementation of action sequences by a neostriatal site: a lesion mapping study of grooming syntax

The neostriatum and its connections control the sequential organization of action ("action syntax") as well as simpler aspects of movement. This study focused on sequential organization of rodent grooming. Grooming syntax provides an opportunity to study how neural systems coordinate natural patterns of serial order. The most stereotyped of these grooming patterns, a "syntactic chain," has a particularly stereotyped order that recurs thousands of times more often than could occur by chance. The purpose of the present study was to identify the crucial site within the striatopallidal system where lesions disrupt the syntax or serial order of syntactic grooming chains without disrupting constituent movements. Small excitotoxin lesions were made using quinolinic acid at bilateral sites within the dorsolateral, dorsomedial, ventrolateral, or ventromedial neostriatum, or in the ventral pallidum or globus pallidus of rats. An objective technique for mapping functional lesions was used to quantify cell death and to map precisely those lesions that disrupted grooming syntax. Our results identified a single site within the anterior dorsolateral neostriatum, slightly more than a cubic millimeter in size (1.3 x 1.0 x 1.0 mm), as crucial to grooming syntax. Damage to this site did not disrupt the ability to emit grooming actions. By contrast, damage to sites in the ventral pallidum and globus pallidus impaired grooming actions but left the sequential organization of grooming syntax intact. Neural circuits within this crucial "action syntax site" seem to implement sequential patterns of behavior as a specific function.

Motor function in a patient with bilateral lesions of the globus pallidus

This study describes the long-term deficits of a patient who, after a toxic encephalopathy, sustained extensive bilateral damage to both segments of the globus pallidus (GP) and the right substantia nigra (SN). There were no signs of lesions of the pyramidal tracts or of other motor structures. The most obvious deficits were an abnormal gait with an exaggerated knee extension and a tendency to fall slowly, especially when pushed backward. In contrast, Romberg's test on an unstable platform was normal, as were long-latency leg reflexes induced by perturbations. Inadequate anticipatory and compensatory postural responses, in particular across the hip and knee joints, and slow movements seemed responsible for the falls. Muscle tone was normal but reflex studies showed signs of abnormal facilitation and inhibition at various levels of the neuraxis. We conclude that the GP and SN lesions caused defective input to premotor cortical and brain stem target zones. Dysfunctioning of these zones leads to improper control of the descending ventromedial motor system responsible for locomotion, postural control, and reflex status. The deficits in upper extremity motor performance included delayed and slow movements, inaccurate amplitudes of ballistic responses, a lack of predictive control, and deficits in bimanual coordination. Sensory feedback, proprioceptive more than visual, played a powerful compensating role in rapid aiming movements. Regional blood flow (studied using 15(O)2) was reduced in multiple frontal cortical regions, among which are the hand areas of the supplementary and premotor cortex. We hypothesize that this reflected impaired functioning of these areas, caused by defective bilateral output from GP and SN, and resulting in the motor deficits of the arm and hand.

Selective sparing of human nucleus accumbens in aging and anoxia

OBJECTIVE

To investigate the effects of aging and anoxia on the nucleus accumbens.

METHODS

The number of neurons in nucleus accumbens and caudate nucleus in 35 patients over 65 and 35 under 65 years, all without neurological or psychiatric disease were counted.

RESULTS

There was no statistically significant difference between the number of neurons in the accumbens in the two groups, but there was a decrease in the number of neurons in the elderly group. There was no reduction in volume of the neuronal nucleoli of the accumbens measured in 12 elderly patients compared to controls. These data suggest a sparing of the accumbens from changes associated with aging. There was relative preservation of the nucleus accumbens in 3 patients with anoxic encephalopathy.

CONCLUSIONS

These results show that accumbens was resistant to both aging and anoxia, the mechanism of which is discussed.

The results, indications, and physiology of posteroventral pallidotomy for patients with Parkinson's disease

In the past, stereotactic surgical intervention for Parkinson's disease was considered indicated only in those patients with active motor manifestations that were refractory to pharmacological therapy, manifestations such as tremor, rigidity, dystonia, and dyskinesia. With the reintroduction and refinement of Leksell's posteroventral pallidotomy, both akinetic and hyperkinetic symptoms are now amenable to surgical treatment. We have analyzed the results of 126 patients who underwent either unilateral (n = 58) or bilateral (n = 68) posteroventral pallidotomies. The Unified Parkinson's Disease Rating Scale and Hoehn and Yahr Staging Scale were used for preoperative and postoperative objective assessments. Postoperative follow-up evaluation occurred initially at 1 week and subsequently at intervals between 1 and 12 months (mean = 4.5 months) after surgery. Although individual motor subscores on the Unified Parkinson's Disease Rating Scale were significantly reduced (n = 126, P < or = 0.01), the most dramatic findings were the reversal of akinetic symptoms and the elimination of dyskinesia and profound "off" periods. These clinical results, combined with intraoperative microelectrode records revealing pallidal neuronal hyperactivity, suggest a reconsideration of the pathophysiology of akinesia and point to possible mechanisms of akinesia improvement by posteroventral pallidotomy in some parkinsonian subgroups.

Abnormal movement related potentials in patients with lesions of basal ganglia and anterior thalamus

Movement-related cortical potentials (MRCPs) were recorded from scalp electrodes during wrist flexion in 15 dystonic patients with bilateral (nine) or unilateral (six) circumscribed lesions in the striatum (eight), pallidum (six), or anterior thalamus (one). The results were compared with those of 10 age-matched healthy volunteers. The early (BP) and late (NS') MRCP components were assessed in terms of their gradients and distribution on the scalp in Cz, C3', and C4'. The gradients of both BP and NS' components were significantly flatter in the patients with bilateral lesions than in the control subjects. Also, the BP gradient was maximum at Cz, and the NS' component was contralaterally predominant in the control subjects but not in the patients. In patients with unilateral lesions, the gradients were flatter (p < 0.05) during movement of the dystonic wrist than during movement of the normal wrist. This difference was significant for BP and NS', regardless of the location of the electrodes. Also, the normal topographic predominance of BP at Cz and of contralateral NS' disappeared. The BP and NS' components of the MRCPs are thought to reflect preparatory activity in the supplementary motor area and the primary motor cortex before movement. Reduced BP and NS' gradients in patients with both bilateral and unilateral lesions of the basal ganglia, which project towards the supplementary motor area, are consistent with this hypothesis. The bilateral nature of these reductions suggests that both the ipsilateral and the contralateral motor cortex are involved in the genesis of the MRCPs and that the dystonia in these patients is associated with impaired motor preparation.