Background
Magnetoencephalography studies have shown that the latency of auditory-evoked neuronal action waveforms (N100 m and N50 m peaks) detected at the temporal cortex ipsilateral to the auditory stimulation is delayed as compared with that detected at the contralateral side. Our recent auditory evoked magnetic fields (AEFs) study has indicated that auditory impulses originated from the unilateral ear first arrive at the contralateral temporal cortex and thereafter reach the ipsilateral temporal cortex through interhemispheric neural connections, thus, leading to the delay of ipsilateral N50 m and N100 m peak-latencies 1 . Such a conduction pathway of auditory impulses makes it possible to measure interhemispheric neural conduction time from the difference of ipsilateral and contralateral N100 m or N50 m peaks. Elderly subjects with chronic dizziness often have depressive state and may later develop cognitive deterioration. In the present study, we measured interhemispheric neural conduction velocity (INCV, m/sec) from the distance between the ipsilateral and contralateral temporal cortices and the difference of ipsilateral and contralateral N50 m peak latencies in elderly patients with chronic dizziness to elucidate whether the grade of INCV is related with depressive mood.
Methods
27 elderly patients (68 ± 12 years of age) complaining of dizzy sensation for more than 6 months were subjected to the study. The presence or absence of depressive mood was estimated with Zung's self-rating depression scale (SDS). The patients were classified into two groups, such as Group A with depressive mood (SDS >50) and Group B without depressive mood (SDS<50). AEFs study was performed using superconducting quantum interference device system (MC-6400, Hitachi Ltd.) with 64 co-axial gradiometer. INCV was calculated from the distance between the ipsilateral and contralateral temporal cortices and the difference of ipsilateral and contralateral N50 m peak latencies. In Group A patients, AEFs study was repeated following antidepressive therapy with selective serotonin reuptake inhibitors (SSRI).
Results
10 patients (Group A) were depressive (SDS: 58. 2 ± 7.6) and the other 17 patients (Group B) were not depressive (SDS: 38.0 ± 5.3). INCV was significantly smaller in Group A (10.3 ± 9.0 msec) than in Group B (23.7 ± 11.3 msec, p<0.05). When analyzed in the entire patients, INCV decreased significantly correlating with SDS scores (r = −0.57, p<0.001). In Group A patients, following antidepressive treatment with SSRI, INCV increased significantly (12.2 ± 8.9 msec, p<0.05), and SDS scores decreased significantly (52.9 ± 11.3, p<0.05).
Comments
The results of the present study suggest that the depressive mood is closely related with the reduction in INCV. The neural conduction velocity may play an important role in determinating the mood condition in elderly subjects.