RTMS Reveals Premotor Cortex Dysfunction in Frontal Lobe Epilepsy

Abstract

Studies of motor cortex excitability provided evidence that focal epilepsies may alter the excitability of cortical areas distant from the epileptogenic zone. In order to explore this hypothesis we studied the functional connectivity between premotor and motor cortex in seven patients with frontal lobe epilepsy and seizure onset zone outside the premotor or motor cortex. Low-frequency subthreshold repetitive transcranial magnetic stimulation was applied to the premotor cortex and its impact on motor cortex excitability was measured by the amplitude of motor-evoked potentials in response to direct suprathreshold stimulation of the motor cortex. Stimulation of the premotor cortex of the non-epileptogenic hemisphere resulted in a progressive and significant inhibition of the motor cortex as evidenced by a reduction of motor evoked potential amplitude. On the other hand, stimulation of the premotor cortex of the epileptogenic hemisphere failed to inhibit the motor cortex. The reduced inhibition of the motor cortex by remote areas was additionally supported by the significantly shorter cortical silent periods obtained after stimulation of the motor cortex of the epileptogenic hemisphere. These results show that the functional connectivity between premotor and motor cortex or motor cortex interneuronal excitability is impaired in the epileptogenic hemisphere in frontal lobe epilepsy while it is normal in the nonepileptogenic hemisphere.