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PubMed1997

Mutations that prevent associative learning in C. elegans.

The nematode Caenorhabditis elegans offers a promising system for the reductionist study of learning and memory. In this article, classical conditioning in C. elegans is demonstrated with a variety of associative learning assays. These assays allowed for the isolation and behavioral characterization of 2 mutant C. elegans lines impaired in associative learning. Both lines show no short-term or long-term associative conditioning; however, they appear relatively normal in tests of nonassociative learning and sensorimotor function. In combination with the well-described genetics and neuroanatomy of C. elegans, the isolation of mutants selectively, yet completely, blocked in associative learning provides the basis for an effective characterization of the cellular and molecular aspects of associative learning.

Animals↗

PubMed1984

Effect of dopamine-depleting brain lesions on suckling and weaning in rats.

Rats given large dopamine-depleting brain lesions as adults exhibit severe impairments in ingestive behavior and sensorimotor function. In contrast to these well-known effects, virtually complete destruction of central dopaminergic neurons produced no such dysfunctions when it occurred in neonates. Indeed, rats continued to suckle and grow, albeit somewhat more slowly, and they could be weaned readily when they were 27 days old. Although most brain-damaged animals did not survive weaning when they were 18 days old, whereas controls exhibited no difficulty, this failure appears to be the consequence of their reduced body weight and related inability to maintain body temperature in a relatively cool environment (22 degrees C). Such premature weaning occurred more successfully when growth was stimulated by rearing brain-damaged pups in small litters or when ambient temperatures were raised to 31 degrees C so as to minimize heat loss. These results demonstrate that the effects of near-total dopamine-depleting brain lesions are considerably less severe when they occur in infants than when they occur in adults, and, consequently, they reveal a capacity for neural plasticity during development that is no longer present at maturity.

Animals↗

PubMed1984

Bilateral cutaneous stimulation of the somatosensory system in hemidecorticate rats.

An enduring somatosensory consequence of extensive neocortex injury in people is "simultaneous extinction," which is an interhemispheric perceptual interaction that is operationally distinguishable from neglect. A cutaneous stimulus presented on the contralateral side of the body is readily detected when presented singly but is actively masked during bilateral stimulation. In hemidecorticate rats, small adhesive stimuli were attached to the radial surface of each forelimb simultaneously, and the latencies to contact and to remove each stimulus were recorded. Neglect of the contralateral stimulus lasted 2-3 days. Thereafter the ipsilateral stimulus was removed first, followed immediately by the contralateral stimulus. This ipsilateral sensorimotor bias lasted several months. Further analysis with unremovable tactile stimuli provided evidence for true extinction. For a limited period (during the first 2 postoperative weeks), the contralateral stimulus did not appear to be detected in the presence of the ipsilateral stimulus. Rather than switching back and forth between the two stimuli, the animals ignored the stimulus on the contralateral limb and persisted in their attempts to remove the ipsilateral stimulus. A key feature of the "extinction" was its complete reversibility. Simply by adjusting the sensory fields occupied by the contralateral (C) and ipsilateral (I) stimuli (specifically, by increasing the C/I ratio), the sensorimotor bias was totally shifted to contralateral. During recovery, the size of the C/I ratio necessary to reverse sensorimotor asymmetry gradually decreased. Asymmetrical sensorimotor behavior and amphetamine-induced circling were examined in three additional groups of hemidecorticate rats, which were given their initial behavioral tests at 2, 12, or 52 postoperative weeks. This experiment confirmed the above findings and controlled for practice. Over the course of a year, apparently complete recovery occurred; however, there were residual effects. At each period, previously recovered symptoms were reinstated simply by turning on the room lights and opening the home cage slightly. These data underscore the importance of detailed behavioral analysis and the value of the rat as a model in studies of recovery of sensorimotor function.

Afferent Pathways↗

PubMed1976

Roles of anoxia and noise-induced hearing loss in the postictal refractory period for audiogenic seizures in mice.

The present series of experiments demonstrated a postictal refractory period for audiogenic seizures in DBA/2J mice, which was not related to hearing loss but apparently was related to anoxia. Unlike many previous studies, Experiment 1 controlled for the effects of noise exposure upon hearing sensitivity and demonstrated reduced susceptibility to subsequent audiogenic seizures for at least 1 hr after initial clonic-tonic convulsions. The postictal refractory period was shown to result from the occurrence of seizures per se, not from noise exposure alone. Experiment 2 demonstrated deficiencies of sensorimotor functions that accompanied reduced postictal seizure susceptibility. The two phenomena had similar time courses of recovery, which suggested a common mechanism, probably anoxia, associated with the initial convulsions. In support of this view, Experiment 3 showed that recovery from both phenomena was expedited by allowing subjects to breathe increased O2. The role of anoxia in fatal convulsions was suggested by the finding that subjects experiencing clonic-tonic convulsions in a high-O2 environment survived without exception. In contrast, seizures of air-breathing controls were almost always fatal. Taken together, the data indicate that the postictal reduced susceptibility to audiogenic seizures was closely related to metabolic depletion (in particular, anoxia). The pattern of recovery of susceptibility further suggests that the effects of anoxia impair the spread of seizure activity through the central nervous system, although the initiation of seizures is also affected for a short time.

Anesthesia, Inhalation↗

PubMed1990

The relationship between global and local changes in PET scans.

In order to localize cerebral cognitive or sensorimotor function, activation paradigms are being used in conjunction with PET measures of cerebral activity (e.g., rCBF). The changes in local cerebral activity have two components: a global, region independent change and a local or regional change. As the first step in localizing the regional effects of an activation, global variance must be removed by a normalization procedure. A simple normalization procedure is division of regional values by the whole brain mean. This requires the dependence of local activity on global activity to be one of simple proportionality. This is shown not to be the case. Furthermore, a systematic deviation from a proportional relationship across brain regions is demonstrated. Consequently, any normalization must be approached on a pixel-by-pixel basis by measuring the change in local activity and change in global activity. The changes associated with an activation can be partitioned into global and local effects according to two models: one assumes that the increase in local activity depends on global values and the other assumes independence. It is shown that the increase in activity due to a cognitive activation is independent of global activity. This independence of the (activation) condition effect and the confounding linear effect of global activity on observed local activity meet the requirements for an analysis of covariance, with the "nuisance" variable as global activity and the activation condition as the categorical independent variable. These conclusions are based on analysis of data from 24 scans: six conditions over four normal subjects using a verbal fluency paradigm.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1997

Motor cortical mapping of proximal upper extremity muscles following spinal cord injury.

Focal transcranial magnetic stimulation was used to map the motor cortical representations of the relaxed and gently contracted biceps brachii, deltoid and triceps muscles in 22 subjects comprised of 12 controls, five subjects with complete and five with incomplete cervical spinal cord lesions (SCI). Motor evoked potentials (MEPs) were rarely observed during the resting condition (3/30 muscles tested; SCI group) which precluded detailed analysis of these data. With background facilitation, the mean number of scalp stimulation sites producing MEPs varied according to muscle (P < 0.001); biceps yielded the largest maps and triceps the smallest. The cortical representations of proximal upper extremity muscles were largest for the control group and smallest for the incomplete SCI group although differences were not significant (P > 0.09). The optimal site of stimulation (that which produced the largest MEP) was always surrounded by an area producing submaximal MEPs, but was variable across subjects and groups. There was extensive overlap in the motor cortical representation areas corresponding to the three muscles of interest. Following maximal intensity stimulation at the optimal site, the mean MEP amplitudes (normalized) were largest for the biceps muscle and smallest or absent in triceps (P < 0.02). No differences were detected between groups (P > 0.50). The threshold stimulus intensity was highest for those with incomplete SCI and lowest amongst control subjects (P < 0.05), with biceps then deltoid muscles generally having lower thresholds than triceps (P < 0.001). The findings suggest that cortical map areas and MEP characteristics are not significantly altered in gently contracting muscles innervated by nerve roots rostral to the lesion. Only activation thresholds are higher following SCI, particularly incomplete lesions, although there is no apparent association with sensorimotor function. The inability to elicit MEPs in the relaxed muscles of patients with SCI fail to support previous reports of expanded motor cortical representations associated with muscles innervated by roots rostral to the lesion.

Adult↗

PubMed1991

Mirror-reversal phenomena in the cutaneous perception and writing of children.

When a letter is drawn on the forehead, it is perceived cutaneously as a mirror reversal of the experimenter-defined stimulus. An analogous mirror-reversal phenomenon is found in motor behaviour; eg, writing on the downward-facing horizontal surface of a table. We examined these mirror-reversal phenomena in tasks, performed by 4-year-old and 8-year-old children, involving cutaneous perception and motor-production. The children's tendencies toward mirror reversal in the two tasks varied with the orientation and position of the surface, but were similar to those of sighted and blind adult subjects. In addition, mirror reversal was independent of the left-right indifference often observed in young children in writing or visual-matching tasks. The implications of these findings are discussed in the context of a body schema used to guide sensorimotor functions.

Attention↗

PubMed1986

Construct validity of the Kendrick Battery with institutionalized aged.

In this study, we attempted to explore the construct validity of the Kendrick Battery by using an American sample and psychometric tests as indexes of diffuse organicity, depression, and normality. Institutionalized residents (N = 53) were tested twice (6-week interval). When organicity was defined by disorientation and memory deficits, then both the Object Learning test and the Digit Copying test were accurate in differentiating preestablished criterion groups. When organicity was defined more broadly, including sensorimotor function, the Digit Copying test alone was more accurate when depression was defined in terms of irritability, restlessness, and despair. These data suggest that although the Kendrick scales appeared to be sensitive to organicity and depression in this sample, their validity varied with the criteria for each when such were defined psychometrically.

Aged↗

PubMed1991

Postural stability and associated physiological factors in a population of aged persons.

A battery of 13 visual, vestibular, sensorimotor, and balance tests was administered to 95 elderly persons (mean age 82.7 years) to examine the relationships between specific sensorimotor functions and measures of postural stability. When subjects stood on a firm surface, increased body sway was associated with poor tactile sensitivity and poor joint position sense. When subjects stood on a compliant surface (which reduced peripheral sensation) with their eyes open, increased body sway was associated with poor visual acuity and contrast sensitivity, reduced vibration sense, and decreased ankle dorsiflexion strength as well as reduced joint position sense. Increased body sway with eyes closed on the compliant surface was associated with poor tactile sensation, reduced quadriceps and ankle dorsiflexion strength, and increased reaction time. Poor performance in two clinical measures of postural stability was associated with reduced sensation in the lower limbs as measured by joint position sense, tactile sensitivity and vibration sense, reduced quadriceps and ankle dorsiflexion strength, and slow reaction times. The prevalence of vestibular impairments was high in this group, but vestibular function was not significantly associated with sway under any of the test conditions. The results suggest that reduced sensation, muscle weakness in the legs, and increased reaction time are all important factors associated with postural instability. An analysis of the percentage increases in sway under conditions where visual and peripheral sensation systems are removed or diminished, compared with sway under optimal conditions, indicated that peripheral sensation is the most important sensory system in the maintenance of static postural stability.

Aged↗

PubMed1976

Phantom limb phenomenon in patients with leprosy.

The phantom limb phenomenon (PLP) was studied in 42 patients with leprosy who had limb amputation and/or digital shortening; some of the patients also had another type of limb deformity, such as claw-hand or foot-drop, which did not involve significant loss of tissue. Thirty-eight (90 per cent) of the patients reported having at least one phantom limb (PL) for a missing or deformed part. Associated with each of the three types of limb defects, two descriptively and experientially distinct types of PLs were found: the paresthetic or typical (TPL) and the painless or natural (NPL). Descriptions of the TPL and the NPL are given. The findings were compared to various reports, particularly those of Stetter and Frederiks. The leprosy TPL was similar both to the PL of amputees as frequently described in the literature, and to what Stetter and Frederiks termed the PL sensations. A close correspondence, if not identity, was noted between the NPL of leprosy patients and the equivalent categories of Stetter's PL experience and Frederiks' PL as such. Included in these three designations are aspects of the PLP that are associated with the normal, intact limb; these aspects are thought to be usual concomitants of the PLP and to constitute manifestations of the persistence of the normal body image. From our findings, we conclude that for the appearance of a PLP, the actual loss of a part of a limb, whether slow or sudden, is not required, but the loss of its sensorimotor functions is sufficient.

Adult↗

PubMed1991

Prognostic significance of cerebral status: dimensions of clinical outcome.

This report examines the relationship between a set of neurobehavioral predictor variables (premorbid cognitive-perceptual abilities, sensorimotor functions, and complex integrative skills) and three dimensions of clinical outcome (social outcome, work functioning, and rehospitalization) 2 years after discharge from inpatient treatment for a group of psychiatric disorders. Results indicated the strongest relationship was between premorbid ability levels and work performance, particularly maintaining stability of employment or work role function. This finding is discussed from the standpoint of neurological processes underlying early acquisition of basic cognitive-perceptual skills in the prediction of outcome.

Adult↗

PubMed1991

Herniated L4-L5 disc after placement of Harrington instrumentation for a fracture of the thoracolumbar spine.

The authors report a case in which L5 radiculopathy developed acutely after surgery for placement of Harrington rod instrumentation for an L1 body fracture. Computed tomographic myelography demonstrated a large L4-L5 herniated disc that had not been present in preoperative studies. An emergency laminectomy was performed, and a large, free, subligamentous disc fragment was removed. The patient subsequently regained L5 sensorimotor function. The postoperative development of lumbar radiculopathy is an uncommon complication of Harrington rod instrumentation that may result from several biomechanical features of the instrumentation. These injuries may not be detected by intraoperative monitoring of somatosensory evoked potentials, and therefore, the postoperative neurological examination assumes a crucial role in the early diagnosis of these lesions. As our case demonstrates, these radicular deficits may be reversible if their cause is promptly recognized and treated.

Aged↗

PubMed1989

Pathogenesis of spinal cord injury and newer treatments. A review.

Many victims of traumatic spinal cord injury (SCI) suffer immediate paralysis as well as a subsequent progressive worsening of the cord pathology. Certain sensorimotor functions that might otherwise have returned are irreversibly lost because of this delayed response. An understanding of the pathophysiology behind this progressive, self-destructive sequence is yet to be acquired; however, numerous proposals have been set forth involving processes such as edema formation, vascular changes, an inflammatory reaction, and destruction of the neuronal plasma membranes. In this review, the authors outline many of the chemical, anatomic, and functional changes associated with SCI as well as a number of treatment regimens that have been found to improve recovery from SCI (including parenteral glucocorticoid therapy, localized cord cooling, calcium channel blockers, and opiate antagonism). From this, a number of mechanisms accounting for the mediation and/or prevention of the secondary destructive response are synthesized.

Animals↗

PubMed1995

Evaluation of saccadic eye movements as an objective test of recovery from anaesthesia.

Saccadic eye movements have been previously used to assess residual effect of anaesthetics, but this test is seldom compared to other psychomotor tests. The aim of the present study was to validate saccades as a recovery index in relation to frequently referred subjective and psychometric tests. Eight healthy subjects were tested before and after intra-muscular injection of either placebo or 0.15 mg.kg-1 of midazolam. Each session consisted of a saccadic test (recorded by electro-oculography), a choice-reaction-time test (CRT), a subjective state-of-alertness test (11 visual analogic scales) and blood sampling (to monitor midazolam plasma concentration), before and 30 (t30), 60 (t60), 120 (t120), 180 (t180), 240 (t240) minutes after drug administration. In the placebo group, there was no change in subjective assessment, saccade characteristics (latency, peak velocity and duration) or CRT results. In the midazolam group, 6 subjective items changed with different time-courses, when compared to baseline: from t30 to t120 (drowsy, in shape, tired, clumsy, strong) and t120 (woolly). Saccade latency and duration were significantly different from t30 to t120 and until t180 for peak velocity. CRT performance was significantly altered from t30 to t120. Midazolam plasma concentration decreased from 177 +/- 33 ng.ml-1 at t30 to 47 +/- 12 ng.ml-1 at t240. At this latter time, sensorimotor functions returned to the baseline. All subjects fulfilled the clinical conditions for home discharge 4 hours after administration. These results suggest that a saccadic eye movement test is a sensitive and reliable tool for the assessment of residual effect of anaesthetics. This test was found to be more sensitive than CRT test since peak saccadic velocity was the last psychometric parameter to be returned to baseline after midazolam injection. This study also confirms the poor reliability of subjective assessment, as subjects tended to underestimate the alteration of their performance immediately following drug injection.

Adult↗

PubMed1995

The effect of a 12-month exercise trial on balance, strength, and falls in older women: a randomized controlled trial.

OBJECTIVE: To determine whether a 12-month program of regular exercise can improve balance, reaction time, neuromuscular control, and muscle strength and reduce the rate of falling in older women. DESIGN: A randomized, controlled trial of 12 months duration. SETTING: Conducted as part of the Randwick Falls and Fractures Study in Sydney, Australia. PARTICIPANTS: One hundred ninety-seven women aged 60 to 85 years (mean age 71.6, SD = 5.4) who were randomly recruited from the community. OUTCOME MEASURES: Accidental falls, postural sway, reaction time, neuromuscular control, and lower limb muscle strength. MAIN RESULTS: Exercise and control subjects were tested before, midway through, and at the end of the trial. At initial testing, exercisers and controls performed similarly in all tests and were well matched in relevant health and lifestyle factors. The mean number of classes attended for the 75 exercise subjects who completed the program was 60.0 (range 26-82). At the end of the trial, the exercise subjects showed improved performance in all five strength measures, in reaction time, neuromuscular control, body sway on a firm surface with the eyes open, and body sway on a compliant surface with the eyes open and closed. In contrast, there were no significant improvements in any of the test measures in the controls. In one test measure, hip flexion strength, the exercisers showed continued improvement throughout the study year. There was no significant difference in the proportion of fallers between the exercise and control subjects. Interesting trends were evident, however, between falls frequency and adherence to the exercise program. CONCLUSIONS: These findings show that exercise can produce long-term benefits with regard to improving sensorimotor function in older persons. The findings also suggest that high compliance to an exercise program may reduce falls frequency, although further studies are required to conclusively demonstrate that exercise offers an effective means of preventing falls.

Accidental Falls↗

PubMed1997

Influence of spinal cord injury on cerebral sensorimotor systems: a PET study.

OBJECTIVES: To assess the effect of a transverse spinal cord lesion on cerebral energy metabolism in view of sensorimotor reorganisation. METHODS: PET and 18F-fluorodeoxyglucose were used to study resting cerebral glucose metabolism in 11 patients with complete paraplegia or tetraplegia after spinal cord injury and 12 healthy subjects. Regions of interest analysis was performed to determine global glucose metabolism (CMRGlu). Statistical parametric mapping was applied to compare both groups on a pixel by pixel basis (significance level P = 0.001). RESULTS: Global absolute CMRGlu was lower in spinal cord injury (33.6 (6.6) mumol/100 ml/min (mean (SD)) than in controls (45.6 (6.2), Mann-Whitney P = 0.0026). Statistical parametric mapping analysis disclosed relatively increased glucose metabolism particularly in the supplementary motor area, anterior cingulate, and putamen. Relatively reduced glucose metabolism in patients with spinal cord injury was found in the midbrain, cerebellar hemispheres, and temporal cortex. CONCLUSIONS: It is assumed that cerebral deafferentiation due to reduction or loss of sensorimotor function results in the low level of absolute global CMRGlu found in patients with spinal cord injury. Relatively increased glucose metabolism in brain regions involved in attention and initiation of movement may be related to secondary disinhibition of these regions.

Adult↗

PubMed1980

Postural dependence of reaction time after a VL thalamotomy.

Postural dependence of the EMG-RT of the triceps brachii muscles was measured in 68 parkinsonian patients of which 38 underwent a ventrolateral thalamotomy. A thalamotomy did not affect patients' EMG-RT per se, but it changed the postural dependence of the EMG-RT. After left thalamotomy the position changes of both shoulders did not influence the EMG-RT of the right triceps, and after right thalamotomy the position change of the left shoulder had no influence on the EMG-RT of both triceps. As for the sensorimotor function, it is assumed that the right thalamus has bilateral control on the input system and the left thalamus has bilateral control on the output system.

Adult↗

PubMed1992

Physiological factors associated with injurious falls in older people living in the community.

Performance in six tests of sensorimotor function was measured in 50 subjects who were admitted to an acute hospital because of a fall (ICD codes E880-888), but who did not suffer a fracture of the lower limbs as a result. Performances in these tests were compared with 50 subjects of the same age and sex who had not fallen in the previous 12 months. It was found that those admitted to hospital because of a fall had decreased tactile sensation, reduced quadriceps strength and increased body sway on firm and compliant surfaces. The fallers also performed poorly in clinical tests of static and dynamic balance. Psychoactive-drug use was associated with falling and a number of test measures, including body sway, static balance, dynamic balance and quadriceps strength. Twenty-seven percent of fallers had poor outcomes, in that 1 year after testing, they had either suffered three or more additional falls, been readmitted to hospital, been transferred to nursing homes or died.

Accidental Falls↗