Abnormal somatosensory processing may contribute to motor impairments observed in Parkinson's disease (PD). Dopaminergic medications have been shown to alter somatosensory processing such that tactile perception is improved. In PD, it remains unclear whether the temporal sequencing of tactile stimuli is altered and if dopaminergic medications alter this perception.
Somatosensory tactile perception was investigated using temporal order judgment in patients with Parkinson's disease on and off dopaminergic medications and in aged-matched healthy controls. Measures of temporal order judgment were acquired using computer controlled stimulation to digits 2 and 3 on the right hand and subjects were required to determine which stimuli occurred first. Two experimental tasks were compared, temporal order judgment without and with synchronization whereby digits 2 and 3 were vibrated synchronously in advance of the temporal order judgment sequence of stimuli.
Temporal order judgment in PD patients off and on medications were similar to controls. Temporal order judgment preceded by synchronous vibration impaired tactile acuity in controls and in PD off medications to similar degrees, but this perceptual impairment by synchronous vibration was not present in PD patients on medications.
These findings suggest that dopamine in PD reduces cortico-cortical connectivity within SI and this leads to changes in tactile sensitivity.