Discussion
chronic-phase central somatosensory disturbance, neuronal synchronization, bleeding, stroke, neoplasms, Minamata disease, infarction
DISORDER, BRAIN ATROPHY, BLEEDING, STROKE, DYSPLASTIC, NEOPLASMS, DISEASES, PATHOPHYSIOLOGY, DISORDERS, BRAIN TUMORS, MULTIPLE SCLEROSIS, UNILATERAL POLYMICROGYRIA, DEMYELINATION, MINAMATA DISEASE, INFARCTION
We performed single-trial analysis of SEFs to explore the pathophysiological mechanisms of central somatosensory disturbance in patients with chronic MD. Detailed analyses of SEFs under restricted vicinity of the N20m (peak latency ± 3.0 ms) characterized the altered SI response and early somatosensory cortical processing. In this study, the non-response rate and P20m rate were significantly higher in patients with MD than in controls, thereby indicating an impaired SI response. In addition, we observed a significant reduction of the N20m amplitude, cross-correlation value, and gamma response in patients with chronic MD, reflecting a functional abnormality of early somatosensory cortical processing. Therefore, these SEF parameters may shed light on the pathophysiology of minute central somatosensory disturbance in chronic MD.Single-trial analyses have the potential to uncover meaningful brain dynamics that are obscured using the conventional method (averaging brain activity across trials) (In this study, the N20m amplitude on either side was significantly reduced in patients with chronic MD (p One may argue that it is unclear whether the strength of the correlation between the averaged sensor SEFs and SEFs at single-trial epochs results from the amplitude of SEFs or increase of the background 1/f noise in chronic MD. As shown in The P20m peak and an absent N20m peak were observed in 6 and 11 patients with MD, respectively. The latencies of N20m in the averaged SEFs of N20m and P20m epochs in the averaged SEFs of P20m epochs were almost identical (P20m is occasionally observed in unilateral polymicrogyria, a rare dysplastic disorder. Ishitobi et al. recognized P20m in two of five patients with unilateral polymicrogyria in the parietal region (Researchers have recognized the decreased variability of neural activities across trials (increased reproducibility) as a general property of sensory perception (Gamma oscillations emerge from the precise synaptic interactions of excitatory pyramidal cells and inhibitory gamma-aminobutyric acid-ergic interneurons (The cross-correlation value and power strength of the induced gamma oscillations displayed the highest negative correlation with the non-response rate and P20m rate, suggesting that the reduced reproducibility of N20m and gamma oscillations played an important role in the impaired SI response in patients with chronic MD. For both SEF parameters involved in early somatosensory cortical processing, we observed a strong correlation between the cross-correlation value and power strength of the induced gamma oscillations. This finding may be attributed to their close neurophysiological actions (early neuronal synchronization in somatosensory processing).We performed an ROC analysis to evaluate the ability of each parameter to discriminate between controls and patients with MD. The AUC was > 0.7 for all parameters; therefore, each SEF parameter displayed a moderate discrimination ability. Because the confidence intervals of the AUCs overlapped with each other, each SEF parameter was considered to exhibit an approximately equivalent discrimination ability. In other words, these SEF parameters may be useful for detecting chronic-phase central somatosensory disturbance.Our study had some limitations. First, the relatively small sample size may reduce the statistical power of this study. The first patients with MD were officially identified in 1956, and the number of surviving patients is gradually decreasing (<225 survivors of confirmed Minamata disease in Kumamoto prefecture). We recruited 49 patients with MD; therefore, the current sample may be broadly representative of chronic MD. Second, we did not analyze other central somatosensory disorders, such as multiple sclerosis, stroke, and brain tumors. Organic changes in the somatosensory pathway running from the thalamus to the SI accompanied by neoplasms, demyelination, bleeding, and infarction are generally observed on brain MRI scans in patients with these diseases. In contrast, there are no organic changes other than brain atrophy in the SI in patients with MD (