Paired-pulse inhibition in the auditory cortex in Parkinson's disease and its dependence on clinical characteristics of the patients

Abstract

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.

Figure 1

Cortical auditory evoked potentials at paired-pulse stimulation with interstimulus intervals 700 and 900 ms in the age-matched healthy subject and in the patient with Parkinson's disease (PD). N1 (I), P2 (I)—the components of evoked potentials on the first conditional and N1 (II), P2 (II)—on the second test stimuli. In the PD patient, the N1-P2 complexes appearing on second stimuli have greater amplitudes, hence the postexcitatory inhibition is reduced compared to control subject. Vertical solid bars correspond to the onset of auditory signals. Numerals in % represent value of paired-pulse inhibition calculated using the following formula: (A1 − A2)/A1∗100 where A1 and A2 are amplitudes of the N1 (I)/ P2 (I) and N1 (II)/ P2 (II) components, respectively.

Figure 2

Correlation of the averaged value of the paired-pulse inhibition (evaluated for ISIs of 500, 700, and 900 ms) and age of the healthy age-matched subjects. rS is a coefficient of nonparametric Spearman rank-order correlation. N:-number of control subjects.