Somatosensory cortex stimulation for deafferentation pain.

Functional neuroimaging has demonstrated that a relationship exists between the intensity of deafferentation pain and the degree of deafferentation-related reorganization of the primary somatosensory cortex. It has also revealed that this cortical reorganization can be reversed after the attenuation of pain. Deafferentation pain is also associated with hyperactivity of the somatosensory thalamus and cortex. Therefore, in order to suppress pain, it seems logical to attempt to modify this deafferentation-related somatosensory cortex hyperactivity and reorganization. This can be achieved using neuronavigation-guided transcranial magnetic stimulation (TMS), a technique that is capable of modulating cortical activity. If TMS is capable of suppressing deafferentation pain, this benefit should be also obtained by the implantation of epidural stimulating electrodes over the area of electrophysiological signal abnormality in the primary somatosensory cortex. The first studies demonstrated a statistically significant pain suppression in all patients and a clinically significant pain suppression in 80% of them. This clinical experience suggests that somatosensory cortex stimulation may become a neurophysiology-based new approach for treating deafferentation pain in selected patients. In this chapter, we review the relevant recent reports and describe our studies in this field.

Auditory cortex stimulation for tinnitus.

Functional imaging techniques have demonstrated a relationship between the intensity of tinnitus and the degree of reorganization of the primary auditory cortex. Studies in experimental animals and humans have revealed that tinnitus is associated with a synchronized hyperactivity in the auditory cortex and proposed that the underlying pathophysiological mechanism is thalamocortical dysrhythmia; hence, decreased auditory stimulation results in decreased firing rate, and decreased lateral inhibition. Consequently, the surrounding brain area becomes hyperactive, firing at gamma band rates; this is considered a necessary precondition of auditory consciousness, and also tinnitus. Synchronization of the gamma band activity could possibly induce a topographical reorganization based on Hebbian mechanisms. Therefore, it seems logical to try to suppress tinnitus by modifying the tinnitus-related auditory cortex reorganization and hyperactivity. This can be achieved using neuronavigation-guided transcranial magnetic stimulation (TMS), which is capable of modulating cortical activity. If TMS is capable of suppressing tinnitus, the effect should be maintained by implanting electrodes over the area of electrophysiological signal abnormality on the auditory cortex. The results in the first patients treated by auditory cortex stimulation demonstrate a statistically significant tinnitus suppression in cases of unilateral pure tone tinnitus without suppression of white or narrow band noise. Hence, auditory cortex stimulation could become a physiologically guided treatment for a selected category of patients with severe tinnitus.

Psychomotor and cognitive performance in nonapneic snorers: preliminary findings.

Snoring is a common phenomenon and a primary symptom in obstructive sleep apnea syndrome, a sleep-related breathing disorder in which neuropsychological function is reported to be impaired. The first purpose of the present study was to compare cognitive and motor function in 25 heavy nonapneic snorers and 26 sleep apneics. As the basis for impairments in heavy nonapneic snorers is still unclear, the influence of nighttime breathing disturbances and morning alertness, respectively, on daytime performance was evaluated too. Nonapneic snorers exhibit more slow wave sleep and tend to have fewer changes in sleep stage than sleep apnea patients, but values for other sleep variables are similar. Snorers also show comparable alertness. Deficits in immediate visual memory and in visuospatial reasoning are not found. However, there are some indications that snorers show decreased manual dexterity and eye-hand coordination for the nonpreferred hand and that they have deficits in focused attention. In addition, snorers may show difficulties in finger-tapping speed. These performance measures tend to be associated with reduced morning alertness, except for the score on focused attention which has a tendency to be related to the nocturnal breathing disturbances.

Neuropsychological functioning and determinants of morning alertness in patients with obstructive sleep apnea syndrome.

Neuropsychological functioning is reported to be impaired in patients suffering from obstructive sleep apnea syndrome (OSAS). This syndrome is characterized by nocturnal respiratory disturbances, blood oxygen desaturations, sleep fragmentation, and excessive daytime sleepiness. Opinions are divided concerning the exact relationship between the observed cognitive deficits, nocturnal hypoxia, sleep disruption, and impaired daytime alertness. In the present study, morning neuropsychological function of 26 moderate to severe middle-aged sleep apneics is compared to that of 22 primary insomniacs. There were no performance differences on a range of neuropsychological tests among the two patient groups. In addition, the data suggest that morning alertness impairment, which is closely associated with a lack of slow wave sleep (SWS) and rapid eye movement (REM) sleep, is of major importance in inducing poorer cognitive performance in patients with moderate to severe sleep apnea.