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Biomedical subjects

D J Beckley

Publications and source records attributed to D J Beckley.

26 records · Page 2Linked to original sources
PubMed1991

Electrophysiological correlates of postural instability in Parkinson's disease.

Postural reflexes in response to sudden toe-up tilts of a supporting forceplate platform were studied in free-standing patients with stage III (N = 5) and stage IV (N = 5) Parkinson's disease and compared to 5 age- and sex-matched normals. Latencies of the short (SL), medium (ML) and long latency (LL) responses were normal in the patients. The normalized mean amplitudes of the ML responses were significantly increased only in the stage IV Parkinson patients (P less than 0.0005). The distal-proximal activation sequence of LL responses observed in all 5 controls was reversed in 1 of the stage III and 4 of the stage IV Parkinson patients. Both the enlargement of the ML response (P less than 0.01) and the inverted activation sequence of LL responses (P less than 0.01) were significantly correlated with severity of the disease. The data establish an association between abnormal modulation of postural reflexes in the lower extremity and clinically rated balance impairment in Parkinson's disease.

Aged↗
PubMed1991

Long latency postural responses are functionally modified by cognitive set.

We examined how cognitive set influences the long latency components of normal postural responses in the legs. We disturbed the postural stability of standing human subjects with sudden toe-up ankle rotations. To influence the subjects' cognitive set, we varied the rotation amplitude either predictably (serial 4 degrees versus serial 10 degrees) or unpredictably (random mixture of 4 degrees and 10 degrees). The subjects' responses to these ankle rotations were assessed from the EMG activity of the tibialis anterior, the medial gastrocnemius, and the vastus lateralis muscles of the left leg. The results indicate that, when the rotation amplitude is predictable, only the amplitude of the long latency (LL) response in tibialis anterior and vastus lateralis varied directly with perturbation size. Furthermore, when the rotation amplitude is unpredictable, the central nervous system selects a default amplitude for the LL response in the tibialis anterior. When normal subjects are exposed to 2 perturbation amplitudes which include the potential risk of falling, the default LL response in tibialis anterior appropriately anticipates the larger amplitude perturbation rather than the smaller or an intermediate one.

Adult↗
PubMed1991

Postural reflexes in patients on long-term neuroleptic medication.

It is not conclusively known whether the amplitude of medium latency postural reflexes is controlled by dopamine. To further assess the influence of supraspinal dopaminergic pathways on postural reflexes, we studied short (SL), medium (ML) and long latency (LL) reflexes in the lower extremity of 10 patients on long term (greater than 6 months) neuroleptic medication, 5 with and 5 without mild drug induced parkinsonism. A control group consisted of 10 age and sex matched healthy volunteers. In both patient groups, latencies and amplitudes of all 3 responses were identical to normal controls. These findings suggest that a moderate postsynaptic inhibition of central dopaminergic pathways is insufficient to cause enhanced amplitudes of ML responses.

Adult↗
PubMed1990

Lack of age effects on human brain potentials preceding voluntary movements.

We examined age effects on Movement related potentials (MRPs) in 13 young (mean age = 29.3 years) and 13 old (mean age = 67.2 years) normal adults in right, left and bimanual self-paced button press conditions. Both the groups generated a slowly rising readiness potential (RP) at about 1000 ms, a negative shift (NS') at about 450 ms and a motor potential (MP) at about 100 ms prior to movement. The RP was symmetrical, bilaterally distributed and maximal at the vertex in all conditions in both the groups. Both the groups produced contralaterally enhanced NS' and MP components in unimanual conditions. In contrast to prior reports, topographical distribution, onset latency and mean amplitude were comparable between young and old subjects for the RP, NS' and MP components of the MRP. The results indicate that motor programming as indexed by MRPs is unaffected by normal aging.

Adult↗