We aimed to determine the value of the paired-pulse inhibition (PPI) in the auditory cortex in patients with Parkinson's disease (PD) and analyze its dependence on clinical characteristics of the patients. The central (Cz) auditory evoked potentials were recorded in 58 patients with PD and 22 age-matched healthy subjects. PPI of the N1/P2 component was significantly (P < .001) reduced for interstimulus intervals 500, 700, and 900 ms in patients with PD compared to control subjects. The value of PPI correlated negatively with the age of the PD patients (P < .05), age of disease onset (P < .05), body bradykinesia score (P < .01), and positively with the Mini Mental State Examination (MMSE) cognitive score (P < .01). Negative correlation between value of PPI and the age of the healthy subjects (P < .05) was also observed. Thus, results show that cortical inhibitory processes are deficient in PD patients and that the brain's ability to carry out the postexcitatory inhibition is age-dependent.
The question of the relationship between contingent negative variation and the mechanisms controlling motor and mental functions has received inadequate study. The aims of the present work were to investigate the relationship between the early and late phases of contingent negative variation and the state of motor and mental functions in patients with Parkinson's disease and to study the effects of levodopa on contingent negative variation. Patients with Parkinson's disease showed significant decreases in the amplitudes and areas of both phases of contingent negative variation as compared with subjects of similar age. Correlation analysis demonstrated a negative relationship between the extent of impairment of coordinatory muscle interactions and the amplitudes of both phases of this variation (p < 0.01). There was a positive relationship between the magnitudes of both phases and the state of mental functions, particularly memory (p < 0.05). Treatment of patients with Parkinson's disease with levodopa was followed by a significant increase in the late phase (p < 0.05). The results obtained here provide evidence for the important role of structures supporting both direct motor control and mental functions in forming both phases of contingent negative variation. The greater effect of levodopa on the late phase of contingent negative variation suggests that the efferent system of the basal ganglia has a greater role in generating the late phase than in organizing the early phase of the variation.
In clinically healthy kinsmen of patients suffering from Parkinson's disease, we studied the amplitude/frequency characteristics of EMG activity recorded from flexors and extensors of the elbow joint in order to reveal symptoms of extrapyramidal insufficiency (EPI) in these persons and to propose necessary recommendations to such a risk group. We examined four groups of persons: group 1 consisting of 37 healthy kinsmen of patients with clinical diagnosis of Parkinson's disease; control group 2 consisting of 20 tested persons whose age was analogous to that of persons of group 1; group 3 including 33 Parkinsonian patients; and group 4 of 24 virtually healthy persons of elderly age, i.e., the group considered to be the control one with respect to group 3. In Parkinsonian patients, the main EPI correlates were the following: (i) significantly increased amplitude of EMG recorded from the arm muscles in the resting state, (ii) bursting discharges in such EMGs generated with a 4-9 sec -1 frequency (type III of EMG), and (iii) abnormally increased coefficients of reflex involvement (CRI) for the muscles of the opposite arm at retention of a load by one arm. One symptom of EPI or another were found in 20 (54.1%) kinsmen of the Parkinsonian patients; in this case, increased EMG amplitudes were observed in 13 persons (35.1%). We also observed significant correlation of the level of rise in the amplitude of the resting EMG with the age of the tested persons. In 29.7% kinsmen of the Parkinsonian patients, burst discharges with a 5-10 sec -1 frequency were present in their EMGs, while in 16.2% of these persons we observed increased CRIs at retention of a load. For comparison, in the corresponding control group, increased amplitudes of the resting EMG, generation of burst EMG dischargers, and increased CRIs were observed in 15, 5, and 10% of the tested persons, respectively. Therefore, in kinsmen of the Parkinsonian patients, some EMG EPI manifestations were observed 2.3 to 5.9 times more frequently that those in the corresponding control group. For the members of the risk group, recommendations concerning the daily routine (mode of life) and the dietary intake, as well as a list of drugs to be avoided for long-term administration, were proposed.
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