Cortical Sensory Dysfunction and the Parietal Lobe

that these findings suggest an aberrant function in the cortical GABAergic inhibitory circuits. Sensory cortex hyperexcitability also appears to be important in the pathophysiology of myoclonus. Measuring cortical potentials in response to peripheral sensory stimulation is commonly performed to study the integrity of the central nervous system and the technique is commonly referred to as SEPs. 'Giant' SEPs (P25–P33) are known to occur in patients with cortical myoclonus and suggest hyperexcitability of the sensory cortex. Similar to the TMS paired pulse paradigm, SEP can also be administered in this fashion. SEP suppression is seen at an ISI of 100 ms in healthy individuals. In some patients with myoclonus, suppression was not observed, and in some cases, facilitation was noted suggesting a dysfunction of the sensory cortical inhibitory circuits leading to hyper-excitability in the cortex. There is ample evidence to suggest aberrant excitabil-ity in the motor and sensory cortices in patients with cortical myoclonus. The underlying pathology though unclear is being studied in great detail using advances in electrodiagnostic techniques. Recent evidence suggests that interhemispheric interactions between the motor cortices appear to be important. The molecular and biochemical abnormalities underlying the hyperexcitab-lity are yet to be defined. Treatment The pharmacological management of cortical myoclonus includes Clonazepam, valproic acid, primidone, and pir-acetam. Newer agents such as Levetiracetam (an analogue of piracetam) and g-hydroxybutyric acid (GHB) are also effective antimyoclonic therapies. Glossary Astereognosia – Inability to recognize things by touch. Exteroception – Perception of stimuli originating outside the body, for example, vision, touch, olfaction. Interoception – Perception of stimuli originating inside the body, for example, hunger, thirst, visceral sensations. Proprioception – Perception of the position and movement of body or its parts. Pseudoathetosis – Involuntary writhing movements due to proprioceptive deficits. Simultanagnosia – Inability to synthesize visual information into a complete picture.