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Prognostic value of electrocorticography (ECoG) spikes for temporal lobectomy outcome
Plenary Abstracts ERP ~~r~~~a~es sf ~ernor~
Scanning in Health and Disease
crania-caudai
march of motor signs in some absences.
studying cortical hyperexcitability G. Bairet. i71e National Hospital for
Neurology and
Neurosurgery
London, UK
The memory-scanning task introduced to experimental psychology by Steinberg in the mid 1960s can be readily adapted for the study of short-term memory using EilPs, The task involves the presentation of a memory set of items (e.g. digits) followed by a probe item which requires a response from the subject indicating whether the probe was a member of the memory set (positive) or not (negative), in general, the latency of a large positive potential at around 500-600 ms after the probe increases with the size of the memory set paralleling the increase in reaction time. Stan‘ and Barret (1987, Brain, 110: 935-959) demonstrated degraded responses to probes in a group of patients with reduced digit span but othenn/ise preserved intellect. The responses in the oddball task for these subjects were normal. Although the positive potential is the most prominent in the response to the probes, it is often an earlier negative shift between about 240 and 400 ms which shows the greatest difference between experimental conditions. There is considerable inter-subject variability in the level of activity during this period (Pelosi et al., 1992, EEG Journal, 84: 344-352) which is highly correlated with scores on tests of intellect (Pelosi et al.. 1992. EEG Journal, 84: 515-520). This last result has important implications for the application of the memory scanning task to clinical populations.
The ~~~~~a1 Silent Period in Narmal Subjects and in Disease A. Berardelli. iii Clinica Neurologica.
% Le llniversitd
30, 00785 Roma. Italia
Transcranial stimulation of the motor cortex produces a silent period lasting approximately 200-300 ms. The beginning of the silent period depends on spinal inhibitov mechanisms (recurrent inhibition and AHP). The later part of the silent period probably results from inhibitory effects at cortical level, although a contribution by post-twitch proptioceptive changes cannot be definitely excluded. Recent evidence shows that in based ganglia conditions the silent period after transcianial stimulation is abnormal. In Parkinson’s disease the duration of the silent period is shorter in comparison to normal subjects; the duration is also shorter when the patients are OFF therapy than when they are ON therapy. These findings suggest a role of the dopaminergic inputs in the cortical SP and an inhibitory action of dopaminergic inputs to motor cortex. On the other hand. in patients with Huntington’s disease the duration of the silent period is longer than normal subjects. The finding that the cortical sileni period is prolonged in Huntington’s disease but decreased in Parkinson’s disease suggests that the duration of the cortical silent period lmay reflect basal ganglia influence over the motor
cortex.
C.D. Binnie. .Maudsley Hospital, London, UK The distinction between generalized and partial epilepsy may appear fundamental to concepts of both epileptic seizures and epilepsy syndromes, and is to a considerable degree based on EEG evidence. The introduction by Jasper and Penfield of the “centrencephalic hypothesis” appeared to provide a unitary physioioqical basis for generalized bilaterally synchronous epileptic activity which was subsequent experimental and clinical evidence, also largely originating from the Montreal school rendered this model untenable. It was replaced by Gloor”s concept of the “generalized cortico-reticular epilepsies” which was postulated a diffusely hyperexcitable cerebral cortex which responded abnormally, with spike-and-wave activity to normal afferents from the reticular formation, which ordinarily give rise to spindles. However, this revised model immediately raises the question of whether epileptogenesis is always (or indeed ever) initiated simultaneously through the locally and rapidiy spread than generaiised seizures amy appear at best to be regional and their distinction born partial seizures with rapid secondary generalization becomes a somewhat arbitrary matter of the rate of propagation. On close inspection the ictal phenomenology of that archetypical aeneralized seizure, the absence, includes features which can be explained only by cerebral dysfunction which is asymmetrical or indeed focal. Versive movements have been reported ifi otherwise clinically and electrographically typical absences which responded selectively to valproate therapy; Stefan. on the basis of careful scrutiny of video recordings, describes an asymmetric
A useful method for
is available in patients with pattern-sensitive
epilepsy; hemifield pattern stimulation in susceptible subjects with idiopathic generalized epilepsy demonstrates an asymmetrical threshold for initiating discharges in some 50%. Paradoxically, it may not yet be possible to abandon the centrencephalic model. as there remains a body of experimental evidence of subcortical onset of certain experimental generalized seizures. Examples include the finding by Rodin of high frequency multiunit brain stem activity preceding cortical involvement in chemically-induced seizures which have been claimed as a model of idiopathic generalized epilepsy. Microinjection of convulsants into the substantia nigra produces generalized seizures. It remains unclear whether a single model can explain all clinical forms of generalized seizures, or indeed whether these have a physiological basis significantly different from partial seizures. The neurobioloyical approach to seizure classification proposed by Berkovic and colleagues may overcome these difficulties, but is unlikely to provide a practical alternative to the ILAE classification as a means of communication.
Seizure Recognition and Suppression N. Birbaumer”, T Elbert, H. Rau. P Wolf. *Un;vers;~oimbingen, Psych., GarfenstraRe 29, D-7400 TUbingen, Germany
C/in
A computerized system for automatic detection of slow brain potentials (d.c. potentials) of the human EEG is described. The system records E to 20 set d.c.-EEG changes per trial and projects these changes on a TV-screen in front of the patient and doctor. EOG-artifacts are eliminated on-line. The epileptic patient’s task is to detect seizure provoking negative ootential shifts and to regulate them “mentally” into positive polarity shifts, which were previously shown to be incompatible with seizure generation. Two controlled trials (one double blind) with 16 drug refractory temporal lobe epileptic patients in each group are described. After 28 hours 1 hour sessions of feedback training during which patients received several thousands cf trials of slow potential feedback, one third of the patients in the experimental group were seizure-free, on third showed significant seizure reduction and one third remained unchanged. The physiological mechanisms of slow potential feedback learning are described. Research was supported by the German Research Society(DFG. SFB 307, Bl).
Prognostic Value of Electrocorticography Temporal Lobectomy Outcome
(
) Spikes for
.
W.T Blume *, 0. Kanazawa, J,P Girvin. University Hospitai, 339 Windermere Road, London, Ont. N6A 5A5, Canada Whether 30 minute pre- and 30 minute post-resection ECoG recordings give clinically useful information was explored in 87 consecutive patients operated under local and neurolept anaesthesia. Demographic data: 46 left temporal, 41 right; mean age 29 years. Twenty-five referentially recorded EEG channels sampled hippocampusiamygdala, temporal convexity, hippocampal gyrus, frontal-panetal operculum, orbital-frontal cortex and insu!a (post-resection only). Spikes were visually counted over the iast 100 seconds of the pre-resection and three 10.minute post-resection epochs. Follow-up duration averaged 39 months, minimum 24 months. Pre-resection spikes occurred most commonly in the hippocampus (HPC). Thirty-eight of 75 (50%) patients with P 5 HPC spikes/l00 set were seizure-free (SF) at follow-up vs. 1 /I 2 (8%) with less frequent HPC spikes. Patients without improvement had distinctly fewer total spikes than any other outcome but spike quantity did not distinguish other outcome categories. Spike abundance outside the planned resection area did not correlate with outcome. Post-resection spikes. Temporal lobectomy reduced overall spike rate by 83-85% for SF, >90% and 50-90% improved outcomes but did not affect spike-rate among unhelped patients. However, post-resection spike rate itself dit not predict outcome, except insuia spikes which were more abundant among favourable outcome groups.
Sleep Physiology in the Eldery R.J. Broughton. 8H6, Canada
Ottawa Generai Hospital, 501 Smyth Road, Olrawa, Ont. KlL
Marked changes of sleep occur with normal aging. A number of important
Scanning in Health and Disease
crania-caudai
march of motor signs in some absences.
studying cortical hyperexcitability G. Bairet. i71e National Hospital for
Neurology and
Neurosurgery
London, UK
The memory-scanning task introduced to experimental psychology by Steinberg in the mid 1960s can be readily adapted for the study of short-term memory using EilPs, The task involves the presentation of a memory set of items (e.g. digits) followed by a probe item which requires a response from the subject indicating whether the probe was a member of the memory set (positive) or not (negative), in general, the latency of a large positive potential at around 500-600 ms after the probe increases with the size of the memory set paralleling the increase in reaction time. Stan‘ and Barret (1987, Brain, 110: 935-959) demonstrated degraded responses to probes in a group of patients with reduced digit span but othenn/ise preserved intellect. The responses in the oddball task for these subjects were normal. Although the positive potential is the most prominent in the response to the probes, it is often an earlier negative shift between about 240 and 400 ms which shows the greatest difference between experimental conditions. There is considerable inter-subject variability in the level of activity during this period (Pelosi et al., 1992, EEG Journal, 84: 344-352) which is highly correlated with scores on tests of intellect (Pelosi et al.. 1992. EEG Journal, 84: 515-520). This last result has important implications for the application of the memory scanning task to clinical populations.
The ~~~~~a1 Silent Period in Narmal Subjects and in Disease A. Berardelli. iii Clinica Neurologica.
% Le llniversitd
30, 00785 Roma. Italia
Transcranial stimulation of the motor cortex produces a silent period lasting approximately 200-300 ms. The beginning of the silent period depends on spinal inhibitov mechanisms (recurrent inhibition and AHP). The later part of the silent period probably results from inhibitory effects at cortical level, although a contribution by post-twitch proptioceptive changes cannot be definitely excluded. Recent evidence shows that in based ganglia conditions the silent period after transcianial stimulation is abnormal. In Parkinson’s disease the duration of the silent period is shorter in comparison to normal subjects; the duration is also shorter when the patients are OFF therapy than when they are ON therapy. These findings suggest a role of the dopaminergic inputs in the cortical SP and an inhibitory action of dopaminergic inputs to motor cortex. On the other hand. in patients with Huntington’s disease the duration of the silent period is longer than normal subjects. The finding that the cortical sileni period is prolonged in Huntington’s disease but decreased in Parkinson’s disease suggests that the duration of the cortical silent period lmay reflect basal ganglia influence over the motor
cortex.
C.D. Binnie. .Maudsley Hospital, London, UK The distinction between generalized and partial epilepsy may appear fundamental to concepts of both epileptic seizures and epilepsy syndromes, and is to a considerable degree based on EEG evidence. The introduction by Jasper and Penfield of the “centrencephalic hypothesis” appeared to provide a unitary physioioqical basis for generalized bilaterally synchronous epileptic activity which was subsequent experimental and clinical evidence, also largely originating from the Montreal school rendered this model untenable. It was replaced by Gloor”s concept of the “generalized cortico-reticular epilepsies” which was postulated a diffusely hyperexcitable cerebral cortex which responded abnormally, with spike-and-wave activity to normal afferents from the reticular formation, which ordinarily give rise to spindles. However, this revised model immediately raises the question of whether epileptogenesis is always (or indeed ever) initiated simultaneously through the locally and rapidiy spread than generaiised seizures amy appear at best to be regional and their distinction born partial seizures with rapid secondary generalization becomes a somewhat arbitrary matter of the rate of propagation. On close inspection the ictal phenomenology of that archetypical aeneralized seizure, the absence, includes features which can be explained only by cerebral dysfunction which is asymmetrical or indeed focal. Versive movements have been reported ifi otherwise clinically and electrographically typical absences which responded selectively to valproate therapy; Stefan. on the basis of careful scrutiny of video recordings, describes an asymmetric
A useful method for
is available in patients with pattern-sensitive
epilepsy; hemifield pattern stimulation in susceptible subjects with idiopathic generalized epilepsy demonstrates an asymmetrical threshold for initiating discharges in some 50%. Paradoxically, it may not yet be possible to abandon the centrencephalic model. as there remains a body of experimental evidence of subcortical onset of certain experimental generalized seizures. Examples include the finding by Rodin of high frequency multiunit brain stem activity preceding cortical involvement in chemically-induced seizures which have been claimed as a model of idiopathic generalized epilepsy. Microinjection of convulsants into the substantia nigra produces generalized seizures. It remains unclear whether a single model can explain all clinical forms of generalized seizures, or indeed whether these have a physiological basis significantly different from partial seizures. The neurobioloyical approach to seizure classification proposed by Berkovic and colleagues may overcome these difficulties, but is unlikely to provide a practical alternative to the ILAE classification as a means of communication.
Seizure Recognition and Suppression N. Birbaumer”, T Elbert, H. Rau. P Wolf. *Un;vers;~oimbingen, Psych., GarfenstraRe 29, D-7400 TUbingen, Germany
C/in
A computerized system for automatic detection of slow brain potentials (d.c. potentials) of the human EEG is described. The system records E to 20 set d.c.-EEG changes per trial and projects these changes on a TV-screen in front of the patient and doctor. EOG-artifacts are eliminated on-line. The epileptic patient’s task is to detect seizure provoking negative ootential shifts and to regulate them “mentally” into positive polarity shifts, which were previously shown to be incompatible with seizure generation. Two controlled trials (one double blind) with 16 drug refractory temporal lobe epileptic patients in each group are described. After 28 hours 1 hour sessions of feedback training during which patients received several thousands cf trials of slow potential feedback, one third of the patients in the experimental group were seizure-free, on third showed significant seizure reduction and one third remained unchanged. The physiological mechanisms of slow potential feedback learning are described. Research was supported by the German Research Society(DFG. SFB 307, Bl).
Prognostic Value of Electrocorticography Temporal Lobectomy Outcome
(
) Spikes for
.
W.T Blume *, 0. Kanazawa, J,P Girvin. University Hospitai, 339 Windermere Road, London, Ont. N6A 5A5, Canada Whether 30 minute pre- and 30 minute post-resection ECoG recordings give clinically useful information was explored in 87 consecutive patients operated under local and neurolept anaesthesia. Demographic data: 46 left temporal, 41 right; mean age 29 years. Twenty-five referentially recorded EEG channels sampled hippocampusiamygdala, temporal convexity, hippocampal gyrus, frontal-panetal operculum, orbital-frontal cortex and insu!a (post-resection only). Spikes were visually counted over the iast 100 seconds of the pre-resection and three 10.minute post-resection epochs. Follow-up duration averaged 39 months, minimum 24 months. Pre-resection spikes occurred most commonly in the hippocampus (HPC). Thirty-eight of 75 (50%) patients with P 5 HPC spikes/l00 set were seizure-free (SF) at follow-up vs. 1 /I 2 (8%) with less frequent HPC spikes. Patients without improvement had distinctly fewer total spikes than any other outcome but spike quantity did not distinguish other outcome categories. Spike abundance outside the planned resection area did not correlate with outcome. Post-resection spikes. Temporal lobectomy reduced overall spike rate by 83-85% for SF, >90% and 50-90% improved outcomes but did not affect spike-rate among unhelped patients. However, post-resection spike rate itself dit not predict outcome, except insuia spikes which were more abundant among favourable outcome groups.
Sleep Physiology in the Eldery R.J. Broughton. 8H6, Canada
Ottawa Generai Hospital, 501 Smyth Road, Olrawa, Ont. KlL
Marked changes of sleep occur with normal aging. A number of important