The amputation of an extremity is commonly followed by phantom sensations that are perceived to originate from the missing limb. The mechanism underlying the generation of these sensations is still not clear although the development of abnormal oscillatory bursting in thalamic neurons may be involved. The theory of thalamocortical dysrhythmia implicates gamma oscillations in phantom pathophysiology although this rhythm has not been previously observed in the phantom limb thalamus. In this study, the authors report the novel observation of widespread 38-Hz gamma oscillatory activity in spike and local field potential recordings obtained from the ventral caudal somatosensory nucleus of the thalamus (Vc) of a phantom limb patient undergoing deep brain stimulation (DBS) surgery. Interestingly, microstimulation near tonically firing cells in the Vc resulted in high-frequency, gamma oscillatory discharges coincident with phantom sensations reported by the patient. Recordings from the somatosensory thalamus of comparator groups (essential tremor and pain) did not reveal the presence of gamma oscillatory activity.
Keywords: AC = anterior commissure; DBS = deep brain stimulation; ET = essential tremor; LFP = local field potential; PC = posterior commissure; PSD = power spectrum density; Vc = ventral caudal somatosensory nucleus of the thalamus; Vim = ventral intermediate nucleus of the cerebellar thalamus; Vop = ventral oral posterior nucleus of the thalamus; deep brain stimulation; functional neurosurgery; gamma oscillations; microelectrode recordings; pain; phantom limb; somatosensory thalamus; ventral caudal nucleus.