- Email: [email protected]
Brain rhythms: Regional specificity and generalized systems
S8
Plenary Abstracts
Quantification of morphological abnormalities has previously relied upon study of sural nerve biopsy. A new method for quantification of known types of motor and sensory nerve fibers will be described using skin biopsy.
Entrapment
Neuropathies
J. Kimura. University of Kyoto, Shogoin Sakyoku, Kyoto 606, Japan Despite the unpredictable nature of traumatic injury, certain individual nerves have predirection to isolated damage. These include the long thorecic, suprascapular, musculocutaneous and axillary nerves in the shoulder girdle, and lateral femoral cutaneous, femoral and sciatic nerves in the pelvic girdle. More distally entrapment syndromes develop at the common sites of chronic or recurrent compression for the radial, median, ulnar, common peroneal and tibia1 nerves, Unusual sites of involvement may suggest rare anomalies such as congenital ring constrictions or other categories of disorders such as multifocal motor neuropathies. Electromyographic examination delineates the exact distribution of denervated muscles in localizing a focal nerve lesion. In demyelinative neuropathy, a reduced recruitment pattern of motor unit potentials signals a conduction block. The pattern of distribution here also helps elucidate the zone of involvement, Nerve conduction studies may detect evidence of demyelination which usually precedes axonal degeneration in a compression neuropathy. Stimulation above and below the suspected site of lesion will document not only the slowing of conduction velocity but also changes in amplitude and area of the muscle or nerve action potential as indices of functional block. Such a pattern of abnormalities often helps differentiate an entrapment syndrome from a diffuse neuropathy.
lntraoperative
Monitoring: The Peripheral
Nerves
C. Krarup. Rigshospitalet, Dept. of Clin. Naurophysiology, Copenhagen 2100, Denmark
Blegdamsvej
9,
Nerve conduction studies in the operating room are carried out with the following goals: (1) to determine if axons in traumatized nerve are in continuity; (2) to determine if regeneration is ongoing in nerves with previous injury; (3) to localize the site of nerve compression or other types of focal nerve pathology in order for adequate release or to perform biopsy; (4) to examine changes in nerve conduction parameters during release of nerve compression or neurolysis; (5) to monitor the functional integrity of peripheral nerve during surgery to remove tumors close to the nerve trunk. The methodology used depends on the problem under consideration and includes: (a) stimulation and recording of the nerve action potential below and above the lesion, (b) stimulation at several sites along the nerve and recording of the motor response to localize focal abnormalities, (c)stimulation of peripheral nerve and recording of centrally conducted responses to determine e.g. whether roots are avulsed. and (d) recording of spontaneous muscle activity to monitor manipulation of the nerve. Several sources of error may variably interfere with the study and include: (i) spread of activation to other parts of the nerve or to other nerves, (ii) shunting of the stimulus current or the recorded response by fluid in the operating field, (iii) main line noise due to adverse recording conditions in the operating room. Provided these limitations are adequately considered, nerve conduction studies in the operating room may be of value in determining the most useful treatment for the patient.
Brain Rhythms: Regional Specificity and Generalized F.H. Lopes da Silva. Dept. ExperimentalZoology, Amsterdam 1098 SM, The Netherlands
Systems
UvA, Kruislaan 320,
EEG signals are the result of the dynamic behaviourof neuronal networks. The occurrence of rhythmic EEG activities depends on a number of parameters that are characteristic of these networks, namely (i) the intrinsic properties of the neurons, (ii) the time constants, (iii) the gain factors, i.e. the strength of synaptic interactions, (iv) the length constants which define the spatial interactions between different assemblies of neurons. These assemblies have essential non-linear properties and may have multiple stable states. Whether a given neuronal network finds itself in one or another stable state depends on the input conditions and on the system’s parameters. Different brain regions contain neuronal networks with specific parameters that determine the characteristics of the corresponding dynamics, and therefore of the
local EEG rhythmic activities. In this lecture, the characteristics of two brarn systems that generate different EEG rhythms are considered, in particular the alpha rhythms of the thalamo-cortical system, the beta rhythms of the neocortex and the theta rhythm of the limbic system. The interaction between specific, i.e. local, and generalized systems will be considered, as well as the transition between normal and abnormal EEG rhythms, such as it occurs during epileptiform seizures with the emergence of chaotic behaviour of the underlying neuronal networks.
Tremor C. H. Lucking. Neuroiogische EL, Germany
Universit~tsklinik,
Hansastr 9, D-7800 Freiburg i.
Tremor is usually subdivided into resting, postural, and kinetic (intention) and mode of innervation of antagonistic muscles tremor. Amplitude, frequency (reciprocally or synchronized) are measured by means of electrophysiological methods. Physiological tremor manifests itself under postural and kinetic conditions and is modified by inertia and stiffness of the limb. It is mainly due to irregularities in the discharge patterns of motor units firing at subtetanic rates, and mechanical reflex oscillations, and is therefore interpreted as peripheral tremor. Among pathological tremors, the essential and Parkinsonian tremor are the most common. Essential tremor is a typical postural tremor, the underlying activi?y of the antagonistic muscles being either reciprocally alternating or synchronized or restricted to the agonist only. Parkinsonian tremor classically is a pure tremor at rest (Type I), but is often composed of a resting tremor and a postural tremor of identical frequency(Type II) and less often combined with a faster postural tremor (Type Ill). Essential tremor with reciprocally alterning muscle activity and Type II of Parkinsonian tremor are frequently characterized by an enhancement of the early component of long latency reflex. Essential and Parkinsonian tremor are independent of limb mechanics and are not modified by mechanical loads. Therefore, an underlying central oscillator is most probable. Such a central oscillator may be localized in various cerebral and spinal structures, Major candidates are the inferior olive and tlie ventrolateral thalamus. Both can act in connection with each other or independently. Results from recordings during stereotaxic surgery in man indicate that the ventrolateral thalamus receives a rhythmical input from cerebellar or brain stem structures which may entrained by the inferior olive.
Critical Analysis of Seizure Classifications H.O. Liiders. Cleveland Clinic Foundation, OH 44 106, USA
9500
EuclidAvenue,
Cleveland,
In 1981 the International Commission for Seizure Classification introduced a greatly simplified seizure classification which has now become the universally accepted International Classification of Epileptic Seizures (ICES). The classification is based on a main dichotomy which divides the seizure into generalized and partial (“focal”) seizures, This dichotomy is of great practical utility since partial seizures all respond equally well to the same anticonvulsants, whereas generalized seizures may require special anticonvulsants depending of the type of generalized seizures. The ICES divides further the partial seizures into simple and complex seizures depending if consciousness is altered or not during the ictal event. This is an easy way to differentiate partial seizures which have a major impact on quality of life (complex partial seizures) and those that usually do not affect quality of life to any significant degree (simple partial seizures). This dichotomy is extremely useful in evaluating the effectiveness of anticonvulsant treatments. Seizure classification is, however, not only essential for pharmacological management of patients with epilepsy. Careful analysis of seizure semiology has been an important diagnostic tool for lateralization and localization of neurological diseases which are associated with epileptic seizures. Seizure semiology has also been used extensively for lateralization and/or localization of epileptic foci in the work-up of patients who are candidates for surgery of epilepsy. The current ICES, however, provides little information about the lateralization/localization of the seizure focus of the seizure spread. In this presentation the shortcomings of the ICES, when used in clinical settings which require precise localization of the focus will be discussed. An alternative seizure classification, which has been used extensively in selected presurgical evaluation centers and which is ideally suited for this objective, will be presented.
Plenary Abstracts
Quantification of morphological abnormalities has previously relied upon study of sural nerve biopsy. A new method for quantification of known types of motor and sensory nerve fibers will be described using skin biopsy.
Entrapment
Neuropathies
J. Kimura. University of Kyoto, Shogoin Sakyoku, Kyoto 606, Japan Despite the unpredictable nature of traumatic injury, certain individual nerves have predirection to isolated damage. These include the long thorecic, suprascapular, musculocutaneous and axillary nerves in the shoulder girdle, and lateral femoral cutaneous, femoral and sciatic nerves in the pelvic girdle. More distally entrapment syndromes develop at the common sites of chronic or recurrent compression for the radial, median, ulnar, common peroneal and tibia1 nerves, Unusual sites of involvement may suggest rare anomalies such as congenital ring constrictions or other categories of disorders such as multifocal motor neuropathies. Electromyographic examination delineates the exact distribution of denervated muscles in localizing a focal nerve lesion. In demyelinative neuropathy, a reduced recruitment pattern of motor unit potentials signals a conduction block. The pattern of distribution here also helps elucidate the zone of involvement, Nerve conduction studies may detect evidence of demyelination which usually precedes axonal degeneration in a compression neuropathy. Stimulation above and below the suspected site of lesion will document not only the slowing of conduction velocity but also changes in amplitude and area of the muscle or nerve action potential as indices of functional block. Such a pattern of abnormalities often helps differentiate an entrapment syndrome from a diffuse neuropathy.
lntraoperative
Monitoring: The Peripheral
Nerves
C. Krarup. Rigshospitalet, Dept. of Clin. Naurophysiology, Copenhagen 2100, Denmark
Blegdamsvej
9,
Nerve conduction studies in the operating room are carried out with the following goals: (1) to determine if axons in traumatized nerve are in continuity; (2) to determine if regeneration is ongoing in nerves with previous injury; (3) to localize the site of nerve compression or other types of focal nerve pathology in order for adequate release or to perform biopsy; (4) to examine changes in nerve conduction parameters during release of nerve compression or neurolysis; (5) to monitor the functional integrity of peripheral nerve during surgery to remove tumors close to the nerve trunk. The methodology used depends on the problem under consideration and includes: (a) stimulation and recording of the nerve action potential below and above the lesion, (b) stimulation at several sites along the nerve and recording of the motor response to localize focal abnormalities, (c)stimulation of peripheral nerve and recording of centrally conducted responses to determine e.g. whether roots are avulsed. and (d) recording of spontaneous muscle activity to monitor manipulation of the nerve. Several sources of error may variably interfere with the study and include: (i) spread of activation to other parts of the nerve or to other nerves, (ii) shunting of the stimulus current or the recorded response by fluid in the operating field, (iii) main line noise due to adverse recording conditions in the operating room. Provided these limitations are adequately considered, nerve conduction studies in the operating room may be of value in determining the most useful treatment for the patient.
Brain Rhythms: Regional Specificity and Generalized F.H. Lopes da Silva. Dept. ExperimentalZoology, Amsterdam 1098 SM, The Netherlands
Systems
UvA, Kruislaan 320,
EEG signals are the result of the dynamic behaviourof neuronal networks. The occurrence of rhythmic EEG activities depends on a number of parameters that are characteristic of these networks, namely (i) the intrinsic properties of the neurons, (ii) the time constants, (iii) the gain factors, i.e. the strength of synaptic interactions, (iv) the length constants which define the spatial interactions between different assemblies of neurons. These assemblies have essential non-linear properties and may have multiple stable states. Whether a given neuronal network finds itself in one or another stable state depends on the input conditions and on the system’s parameters. Different brain regions contain neuronal networks with specific parameters that determine the characteristics of the corresponding dynamics, and therefore of the
local EEG rhythmic activities. In this lecture, the characteristics of two brarn systems that generate different EEG rhythms are considered, in particular the alpha rhythms of the thalamo-cortical system, the beta rhythms of the neocortex and the theta rhythm of the limbic system. The interaction between specific, i.e. local, and generalized systems will be considered, as well as the transition between normal and abnormal EEG rhythms, such as it occurs during epileptiform seizures with the emergence of chaotic behaviour of the underlying neuronal networks.
Tremor C. H. Lucking. Neuroiogische EL, Germany
Universit~tsklinik,
Hansastr 9, D-7800 Freiburg i.
Tremor is usually subdivided into resting, postural, and kinetic (intention) and mode of innervation of antagonistic muscles tremor. Amplitude, frequency (reciprocally or synchronized) are measured by means of electrophysiological methods. Physiological tremor manifests itself under postural and kinetic conditions and is modified by inertia and stiffness of the limb. It is mainly due to irregularities in the discharge patterns of motor units firing at subtetanic rates, and mechanical reflex oscillations, and is therefore interpreted as peripheral tremor. Among pathological tremors, the essential and Parkinsonian tremor are the most common. Essential tremor is a typical postural tremor, the underlying activi?y of the antagonistic muscles being either reciprocally alternating or synchronized or restricted to the agonist only. Parkinsonian tremor classically is a pure tremor at rest (Type I), but is often composed of a resting tremor and a postural tremor of identical frequency(Type II) and less often combined with a faster postural tremor (Type Ill). Essential tremor with reciprocally alterning muscle activity and Type II of Parkinsonian tremor are frequently characterized by an enhancement of the early component of long latency reflex. Essential and Parkinsonian tremor are independent of limb mechanics and are not modified by mechanical loads. Therefore, an underlying central oscillator is most probable. Such a central oscillator may be localized in various cerebral and spinal structures, Major candidates are the inferior olive and tlie ventrolateral thalamus. Both can act in connection with each other or independently. Results from recordings during stereotaxic surgery in man indicate that the ventrolateral thalamus receives a rhythmical input from cerebellar or brain stem structures which may entrained by the inferior olive.
Critical Analysis of Seizure Classifications H.O. Liiders. Cleveland Clinic Foundation, OH 44 106, USA
9500
EuclidAvenue,
Cleveland,
In 1981 the International Commission for Seizure Classification introduced a greatly simplified seizure classification which has now become the universally accepted International Classification of Epileptic Seizures (ICES). The classification is based on a main dichotomy which divides the seizure into generalized and partial (“focal”) seizures, This dichotomy is of great practical utility since partial seizures all respond equally well to the same anticonvulsants, whereas generalized seizures may require special anticonvulsants depending of the type of generalized seizures. The ICES divides further the partial seizures into simple and complex seizures depending if consciousness is altered or not during the ictal event. This is an easy way to differentiate partial seizures which have a major impact on quality of life (complex partial seizures) and those that usually do not affect quality of life to any significant degree (simple partial seizures). This dichotomy is extremely useful in evaluating the effectiveness of anticonvulsant treatments. Seizure classification is, however, not only essential for pharmacological management of patients with epilepsy. Careful analysis of seizure semiology has been an important diagnostic tool for lateralization and localization of neurological diseases which are associated with epileptic seizures. Seizure semiology has also been used extensively for lateralization and/or localization of epileptic foci in the work-up of patients who are candidates for surgery of epilepsy. The current ICES, however, provides little information about the lateralization/localization of the seizure focus of the seizure spread. In this presentation the shortcomings of the ICES, when used in clinical settings which require precise localization of the focus will be discussed. An alternative seizure classification, which has been used extensively in selected presurgical evaluation centers and which is ideally suited for this objective, will be presented.