W54 Pathways and mechanisms for motor cortical control in man and monkey

387

Workshops 4. Electrophysiology of cognition

References

Abstract not available.

[!] Alsterm~k B. & Lundl~rg A. (1992) The C3-C4 propriospinal system: TargetReaching and Food-Taking. in: Muscle Afferents and Spinal Control of Moverm~t, ed. L. Jarni, E. Pierrot-Deseilligny, D. Zytnicki, Pergamon Press, Oxford. [2] Maier M, Illert M, Kirkwood P A, Nielsen J & Lemon R (1996) Is there C3C4 pmpriospinal transmission of corticospinal excitation to primate forearm motoneuroaes? Lack of evidence from the anaesthetized monkey. Eurp. J. Physiol. 431 Suppl 6:OI0

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PERCEPTUAL MOTOR INTEGRATION. A REVIEW AND POSSIBLE APPLICATIONS

G. Mulder. Groningen, The Netherlands

NEUROPHYSIOLOGICAL TIMING OF CONSCIOUS PERCEPTUAL MECHANISMS IN HUMANS

PATHOPHYSIOLOGY OF CEREBELLAR ATAXIA

H.C. Diener, D. Timmann, M. Jueptner. Department of Neurology,

J.E. Desmedt. Brussels, Belgium

University Clinics Essen, Hufelandstr. 55, 45122 Essen, FRG

Abstract not available.

The present understanding of the physiological mechanisms of ataxia and other cerebellar symptoms in humans is still very preliminary. Most textbooks still rely on Gordon Holmes's descriptions, which imply that most cerebeilar symptoms occur together. Patients with well-delineated and purely cerebellar lesions are still rare who are able and willing to serve as subjects. However, the number of experimental studies in patients with cerebellar deficits is increasing. Furthermore, new techniques of functional imaging with positron emission tomography and functional magnetic resonance imaging provide increasing knowledge about the physiological functions of the human cerebellum. This review will describe the features of pathological versus normal limb movements and body posture in human cerebellar disorders. It will attempt to describe the physiology and pathophysiology of motor disturbances as well as the role of the cerebellum in motor learning and timing in as far as they are understood up to now.

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IDENTIFICATION OF COGNITIVE ELECTROGENESIS IN NON-AVERAGED HUMAN BRAIN POTENTIALS

C. Tomberg. Brussels, Belgium Abstract not available. ~ ' ]

MOTOR PLANNING AND ID~I~TION

W. Lang. Universitatsklinikfar Neurologie, Wien, Austria Scalp recordings of electric potentials and magnetic fields provide data which are on-line reflections of brain activity. High temporal resolution of these methods offer the possibility to distinguish between different stages of motor preparation and to specify effects of context, task and instructions in preparatory processes. It has been shown that there is a specific spatio-temporal difference of electric potentials when subjects either repeat the same movement or when they select between movements. Directional attention as well as levels or modes of conscious control have systematic effects on the prepaiation of a movement as shown in EEG data. Complexity of the task to be initiated affects preceding electric potentials but differences among studies indicate that subjects' strategies for movement execution have not been controlled so far. It has been shown that different consequences of a movement result in quite specific changes of pre-movement electric potentials. MEG data indicate that the activation pattern of cortical areas which receive reafferem input is modified in the pre-movement period. Finally, reetmt EEG- and MEG data will be reviewed which have provided evidence for an activation of the primary motor cortex during internal simulation of movements (motor ideation).

5. Motor Control -'~

NEW ASPECTS ON SPINAL CORD MECHANISMS

M. Ulert. Department of Physiology, University of Kiel, Olshausenstr, 40,

D-24098 Kiel, Germany The C3--C4 prospriospinal system of cats [1 ] receives increasing attention in the study of motor control. Investigations in the freely moving cat indicate that the target-reaching movement of the forelimb is structured within this system, whereas the food-taking component primarily depends on the projection from the corticospinal tract to the forelimb motoneurones via the segmental interneurones. X-ray cinemathographic studies show individuated digit movements during food-taking which, accordingly, must be organized in the disynaptic corticospinal projection. It is one of the interesting questions whether or not a comparable C3-C4 propriospinal system exists in the primate. Based on indirect evidence this has been postulated by several authors, but acute studies in the monkey fail so far to prove its presence [2].

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NEUROPHYSIOLOGICAL ASPECTS OF POSTURAL TREMOR

G. Deuschl. Department of Neurology, Christian-Albrechts-University

Kiel, Germany The origin of postural tremor is still unknown although several arguments favor an involvement of olivocerebellar pathways. Animal studies suggest that the olive can function as a central pacemaker, ipsilateral postural tremor is relieved by insults to the cerebellum or stereotactic lesions of the subthalamic or thalamic areas and PET-studies suggest cerebellar hyper-activity to be related with tremulous movements. Symptomatic palatal tremor, a condition associated with olivary pseudohypertrophy, might share similarities with essential tremor, because this tremor is believed to be mediated through the olivo-cerebellar connections. In this case motor disturbances reminiscent to cerebellar dysfunctions can be found in addition to tremulous movement. Thus, if the hypothesis of a relation of palatal tremor with postural tremor holds true, similar dysfunctions have to be expected in essential tremor as the most frequently occurring form of postural tremor. In fact, there is ample evidence for such an abnormality from gait studies. When analyzing the clinical features of postural tremor in a larger group of patients with essential tremor we found a subgroup of patients having clearcut intention tremor as a sign of possible cerebellar dysfunction. It has been shown, that the triphasic pattern of voluntary movements is abnormal in essential tremor as the second agonist is delayed in these patients. When assessing the triphasic pattern in the patients with intention tremor, there is even a delay of the antagonist. In conclusion, there are similarities of electrophysiologic parameters in patients with essential tremor and those with cerebellar disturbances confirming the clinical impression of cerebellar abnormalities in essential tremor.

PATHWAYSAND MECHANISMS FOR MOTOR CORTICAL CONTROL IN MAN AND MONKEY R.N. Lemon. Sobell Department of Neurophysiology, Institute of Neurology, Queen Square, London WCIN 3BG, UK A unique feature of the primate motor system is the direct corticomotoneuronal (CM) projection from motor areas of the cerebral cortex to

Workshop 6. Epilepsy Surgery - Presurgical Evaluation: What Is Really Necessary ?

388

spinal motoneurones. In sub-primates, anatomical evidence suggests that these projections are relatively weak or absent, and good physiological evidence for their existence is so far lacking. In primates, the density of CM projections to hand muscle motor nuclei is correlated with the degree of manual dexterity. In the New World squirrel monkey, with poor dexterity, CM projections are scarce and CM-EPSPs are small and slowly rising, while in the Old World macaque, projections are dense and EPSPs are large and fast. The importance of the CM connections in man are strikingly illustrated by recovering stroke patients studied with TMS. There is little or no recovery of hand function unless there is sparing of the fast corticospinal pathway; in contrast, there can be substantial recovery of shoulder and girdle movements without any sign of responses to TMS. In normal subjects, comparison of the recruitment curves for deltoid and hand muscle motor units by voluntary activation and by TMS again confirm the importance of the CM input for voluntary hand movement.

Reference [1] Porter R and Lemon RN (1993) Corticospinal function and voluntary movement. Oxford University Press pp 428.

6. Epilepsy Surgery - Presurgical Evaluation: What Is Really Necessary? PHARMACORESISTANCE E. Perucca. Clinical Pharmacology Unit, University of Pavia, Pavia, Italy Few terms in clinical epileptology are so frequently used and yet so difficult to define as "pharmacoresistance". In fact, when definitions have been proposed, they have been as variable and numerous as the clinicians making them. How many drugs should be tried before a patient can be labelled as "drug resistant"? At what dosages? In what combinations? There are no univocal answers to these questions, although a case can be made for differentiating pharmacoresistance from pseudo-pharmacoresistance, defined as persistence of seizures due to prescription of a wrong drug (e.g. carbamazepine in juvenile myoclonic epilepsy or ethosuximide in complex partial seizures), inappropriate dosage or dosing schedule, or poor compliance. With respect to "true resistance", a useful classification may derive from the development of a grading system. For example, a patient with recently diagnosed partial seizures unresponsive to the highest tolerated dosage of an appropriate drug may have a 20-30% probability of achieving complete remission with alternative agents, whereas a patient who failed to respond to 3 or 4 drugs sequentially or in combination has probably a less that 5-10% chance of becoming seizure-free on other drugs. Ideally, a grading system should take into account not only drug history but also type of epilepsy and possibly duration of the seizure disorder, although there is no clear evidence that recurrent seizures by themselves can lead to intractability.

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PILEPSY SURGERY - PRESURGICAL EVALUATION: WHAT IS REALLY NECESSARY? MRI

J.S. Duncan. National Hospital for Neurology & Neurosurgery, London,

UK Optimal MR imaging is an absolute prerequisite in presurgical evaluation for epilepsy surgery. A standard protocol includes: A Tl-weighted volume acquisition, with coronal and axial reformatting of the image; oblique coronal proton density and T2-weighted contiguous 5 mm thick images. Quantitation of hippocampal volumes and T2 mapping may help assessment of borderline cases and identify bilateral hippocampal sclerosis. 15% of presurgicai patients are likely to be MRI negative with this protocol and 15% to have dual pathology identified. If standard M R / d o e s not reveal a structural abnormality, a supplementary protocol includes: further post-processing of data already acquired: reformatting in non-standard orientations, 3-D reconstructions. Further data should also be acquired: e.g. FLAIR, use of surface coils, proton MR Spectroscopy.

In the future, functional MR/ will be increasingly used to lateralize

language functions, locate eloquent cortex and to guide neocortical resections. Stereotactic MR Image-guidance systems currently aid surgical resections and in future will be improved by low-field per-operative MRI.

~--~NON INVASIVE EEG & VIDEO MONITORING FOR PRESURGICAL EVALUATION: CAN WE DO WITHOUT IT? W. van Emde Boas. Inst. v. Epilepsiebestrijding, Heemstede, Netherlands A prerequisite for successful resective epilepsy surgery is the precise delineation of the epileptic zone in a resectable area of either hemisphere. Interictal and ictal EEG and clinical seizure semiology traditionally are used for this purpose but there is an growing role of neuro-imaging (MRI, PET, SPECT). The latter, however, can only identify -and localise- structural lesions or functionally impaired brain areas. Only EEG (and MEG) can lend additional support to a clinical diagnosis of epilepsy and only ictal EEG and the concomitant video documentation of clinical behaviour can establish whether the patient is really suffering from socially disabling partial seizures and whether or not the clinical signs and the tocalising features of the EEG are in accordance with the neuroimaging data. In most presurgical evaluation programs a substantial number of patients turns out to suffer from non-epileptic events, including pseudo seizures, and not every lesion is automatically the cause and site of origin of established epileptic seizures. Although it is true that, in some well defined clinical constellations, i.a. the syndrome of mesial temporal lobe epilepsy, medical history, MRI and interictal EEG alone may be sufficient to allow successful surgery, in most patients it is only after extensive ictal monitoring that such constellations can be identified at all with any degree of certainty. Moreover, ictal documentation of EEG and clinical semiology often provides clues, indicating that apparently easy cases, including lesional cases, may be more complicated than expected and may even warrant invasive studies. Despite the undeniable value of modern imaging techniques, therefore, non-invasive interictal and ictal EEG and -possibly even more importantdocumentation of ictal semiology- is here to stay for most, if not all adult patients and many of the children, evaluated for resective surgery of their medically intractable partial seizures.

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INVASIVE ELECTROPHYSIOLOGICAL RECORDINGS OF ICTUAL AND INTERICTUAL ACTIVITY

P. Chauve]. Rennes, France Abstract not available.

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MAGNETOENCEPHALOGRAPHY IN THE PRESURGICAL EVALUATION OF EPILEPSY PATIENTS

C. Baumgartner. Universit?itsklinik fiir Neurologie, Vienna, Austria Magnetoencephalography (MEG) is a new neurophysiological technique which allows the detection of the brain's magnetic fields by means of highly sensitive instruments, the superconducting quantum inference devices (SQUIDs). The spatial resolution of MEG is about 1/3 better compared with scalp-EEG because magnetic fields are not distorted by the resistive properties of the skull and scalp. The introduction of whole-head MEG systems has led to a major technical breakthrough in MEG research. MEG localization estimates of the interictal spike zone have been shown to be within 10 mm of those obtained from invasive recordings. Concerning detection sensitivity, MEG seems to be more sensitive than scalp-EEG for the detection of epileptic discharges arising from lateral neocortex as 3.5 cm-' of synchronized activity seem to be sufficient to produce a detectable MEG signal as opposed to the classical 6 cm 2 proposed for the scalp-EEG. In mesial temporal lobe epilepsy, an average area of 8 cm 2 seems to be necessary to produce a detectable MEG signal. A major limitation of MEG has been the recording of seizures. So far only anecdotal papers of ictal MEG studies have been reported. MEG has been useful to delineate essential brain regions prior to surgical procedures adjacent to central fissure. Acknowledgment: This research was supported by the Fonds zur Frrderung der wissenschaftlicben Forschung Osterreichs (project P10302MED).