Motor cortex excitability in patients with focal epilepsy

We studied the excitability of the motor cortex using, transcranial magnetic stimulation (TMS) in patients with temporal and extratemporal epilepsy. We applied single and paired-pulse TMS to 15 patients with temporal (n = 7), extratemporal (n = 6) and focal epilepsy lateralised to one hemisphere (n = 2). Patients had no antiepileptic drugs in the last 48 h and were seizure free for 4 h prior to testing. We determined the threshold for EMG responses at rest (RMT), the cortically evoked silent period (CSSP) and intracortical inhibition (ICI, intervals of 2-4 ms) and facilitation (ICF, 7-15 ms) and compared the results to those obtained in 17 normal controls. ICI and ICF was reduced in both hemispheres (P < 0.01. ANOVA) compared to the controls. In the hemisphere of seizure origin ('abnormal') there was a reduction of ICF (P < 0.01) and normal ICI, in the 'normal' hemisphere there was a reduced ICI (P < 0.01) and a slight reduction of ICF (P < 0.05). ICF on the 'abnormal' side was reduced (P < 0.05) compared to the 'normal' hemisphere. RMT was increased in two patients, but group comparison of RMT and CSSP showed no significant differences between patients and controls. The results suggest a remote effect of epileptic activity onto the motor cortex leading to an alteration of activity in local inhibitory circuits.

[1]  R. Crowell.  Distant effects of a focal epileptogenic process. , 1970, Brain research.

[2]  K M Jacobs,et al.  Focal epileptogenesis in a rat model of polymicrogyria. , 1999, Journal of neurophysiology.

[3]  D. Bettucci,et al.  Idiopathic Generalized Epilepsy: Magnetic Stimulation of Motor Cortex Time‐Locked and Unlocked to 3–Hz Spike‐and Wave Discharges , 1994, Epilepsia.

[4]  M Hallett,et al.  Effects of phenytoin on cortical excitability in humans , 1997, Neurology.

[5]  Ichiro Kanazawa,et al.  Ipsilateral cortico-cortical inhibition of the motor cortex in various neurological disorders , 1996, Journal of the Neurological Sciences.

[6]  W. Staines,et al.  Efferent projections of the anterior perirhinal cortex in the rat , 1996, The Journal of comparative neurology.

[7]  B. Day,et al.  MOTOR CORTEX EXCITABILITY IN FOCAL AND GENERALIZED EPILEPSY , 1993 .

[8]  A. Berardelli,et al.  Asymmetry of cortical excitability revealed by transcranial stimulation in a patient with focal motor epilepsy and cortical myoclonus. , 1998, Electroencephalography and clinical neurophysiology.

[9]  S. Berkovic,et al.  Cortical excitability and recovery curve analysis in generalized epilepsy , 1999, Neurology.

[10]  J. Rothwell,et al.  Interaction between intracortical inhibition and facilitation in human motor cortex. , 1996, The Journal of physiology.

[11]  C Iani,et al.  Distinguishing forms of generalized epilepsy using magnetic brain stimulation. , 1996, Electroencephalography and clinical neurophysiology.

[12]  B Conrad,et al.  Continuous intrathecal baclofen infusions induced a marked increase of the transcranially evoked silent period in a patient with generalized dystonia , 1998, Muscle & nerve.

[13]  C. Marsden,et al.  Corticocortical inhibition in human motor cortex. , 1993, The Journal of physiology.

[14]  B. Day,et al.  Electric and magnetic stimulation of human motor cortex: surface EMG and single motor unit responses. , 1989, The Journal of physiology.

[15]  Robert S. Fisher,et al.  Animal models of the epilepsies , 1989, Brain Research Reviews.

[16]  E. Wyllie,et al.  The Treatment of Epilepsy: Principles and Practice , 1997 .

[17]  W Paulus,et al.  Transcranial magnetic stimulation: its current role in epilepsy research , 1998, Epilepsy Research.

[18]  J C Rothwell,et al.  Abnormalities of the balance between inhibition and excitation in the motor cortex of patients with cortical myoclonus. , 1996, Brain : a journal of neurology.

[19]  F. Morrell,et al.  Secondary epileptogenesis in man. , 1985, Archives of neurology.

[20]  B. Connors,et al.  Horizontal spread of synchronized activity in neocortex and its control by GABA-mediated inhibition. , 1989, Journal of neurophysiology.

[21]  B. MacVicar,et al.  Imaging the induction and spread of seizure activity in the isolated brain of the guinea pig: the roles of GABA and glutamate receptors. , 1996, Journal of neurophysiology.

[22]  Magdolna B. Szente,et al.  Cellular mechanisms of neocortical secondary epileptogenesis , 1994, Brain Research.

[23]  F. Mascagni,et al.  Corticoamygdaloid and corticocortical projections of the rat temporal cortex: APhaseolus vulgaris leucoagglutinin study , 1993, Neuroscience.

[24]  B. Kapp,et al.  Frontal cortex projections to the amygdaloid central nucleus in the rabbit , 1985, Neuroscience.

[25]  F. Mascagni,et al.  Projections of the medial and lateral prefrontal cortices to the amygdala: a Phaseolus vulgaris leucoagglutinin study in the rat , 1996, Neuroscience.

[26]  K J Werhahn,et al.  Differential effects on motorcortical inhibition induced by blockade of GABA uptake in humans , 1999, The Journal of physiology.

[27]  B W Connors,et al.  Layer‐Specific Pathways for the Horizontal Propagation of Epileptiform Discharges in Neocortex , 1998, Epilepsia.

[28]  C. Wilson,et al.  Paired pulse suppression and facilitation in human epileptogenic hippocampal formation , 1998, Epilepsy Research.

[29]  J. Donoghue.  Plasticity of adult sensorimotor representations , 1995, Current Opinion in Neurobiology.

[30]  B. Meldrum.  Anatomy, physiology, and pathology of epilepsy , 1990, The Lancet.

[31]  P. Rossini,et al.  Non-invasive electrical and magnetic stimulation of the brain, spinal cord and roots: basic principles and procedures for routine clinical application. Report of an IFCN committee. , 1994, Electroencephalography and clinical neurophysiology.

[32]  B. Day,et al.  The effect of magnetic coil orientation on the latency of surface EMG and single motor unit responses in the first dorsal interosseous muscle. , 1994, Electroencephalography and clinical neurophysiology.

[33]  B. Steinhoff,et al.  Effects of antiepileptic drugs on motor cortex excitability in humans: A transcranial magnetic stimulation study , 1996, Annals of neurology.

[34]  B. Day,et al.  Stimulation of the human motor cortex through the scalp , 1991, Experimental physiology.

[35]  C. Capaday,et al.  Input-output properties and gain changes in the human corticospinal pathway , 1997, Experimental Brain Research.

[36]  Propagation of epileptiform potentials in the guinea-pig piriform cortex is sustained by associative fibres , 1996, Epilepsy Research.

[37]  J. Donoghue,et al.  Different forms of synaptic plasticity in somatosensory and motor areas of the neocortex , 1995, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[38]  J. L. Taylor,et al.  The effect of voluntary contraction on cortico‐cortical inhibition in human motor cortex. , 1995, The Journal of physiology.

[39]  A Schnitzler,et al.  The motor syndrome associated with exaggerated inhibition within the primary motor cortex of patients with hemiparetic. , 1997, Brain : a journal of neurology.

[40]  D C Reutens,et al.  Magnetic stimulation of the brain in generalized epilepsy: Reversal of cortical hyperexcitability by anticonvulsants , 1993, Annals of neurology.