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Event related potentials in Alzheimer diseases
the commonest
pathalogy.
In GBS patients
distal latency in median, ulnar
and common peroneal nerves was prolonged while mean motor NC was decreased to 44.12 + 13.7, 46.18 i 17.02 b33.12 jL 10.67 m/set respectively. Thirty five patients (30 M, 5 F) had Arsenic neuropathy. EMG was neurogenic in 80% cases while sural nerve action potential was absent in 14 (40%) instances. Other important categories of PN included hereditary neuropathies (5.3%). nutritional neuropathies (3.8%). collagen vascular disease (5.7%) and post vaccinal neuropathy (3.6%). Clinical and eiectrophysiological details will be discussed and campared with published data from other tropical countries.
otentials in Alzheimer
Diseases
G. Comi. Dept. of Neuroiog~ Scientific Institute U.S. Raffaeale, University of Milan, Via 0lgeOina 60, 211132 Milano, ltalia in this review we will focus on the clinical value of long latency cognitive event-related potentials (ERPs) in dementia of the Alzheimer type (DAT). Most clinical studies on the ERPs have been on the P300 component which has been shown to reflect the fundamental cognitive events, involving stimulus evaluation and immediate memory. There is a general agreement between laboratories that the !atency of P300 is increased and the amplitude is decreased in DAT patients compared to normal controls and patients with other psychiatric conditions, when the comparison is made between groups. What is controversial is the utility of the test as diagnostic procedure. The sensitivity vary from 7% to 83% across reports; differences between the studies in terms of experimental task, methods of analysis and selection of patients and controls contribute to the discrepancy in results. Most clinical studies utilized only a few recording sites, some recent studies suggest that topographic mapping will result in an increase of sensitivity and specificity of P300. DAT is an almost invariable accompaniment of ageing in Down’s syndrome. In Down’s patients P300 latency is increased and amplitude is reduced and the effects of age on P300 are anticipated of about 20 years compared to health population, We recently found that topographic distribution of P3OO is frequently abnormal in Down’s syndrome; the development of dementia in these patients is accompanied by a significant increase of P300 iatency.
l?J. Delwaide. University oftiege, I, 4000 Li&ge, Beigium
H6pital de la Citadeile, Ed. du 12” de Ligne
The neurophysiological mechanisms underlying Parkinsonian rigidity are far from clear. It has first been proposed that changes in gamma innervation could explain Parkrnsonian stiffness but later, an alternative explanation has proposed a hyperactivity in a long loop reflex pathway relaying in the motor cortex. However, the question remains controversial and justifies further studies. We have conducted electrophysiological studies on 70 Parkinsonian patients (39 males; 31 females) at various stages and 49 age-matched controls. We first used magnetic transcranial stimulation to determine the activation threshold and the conditioning of the evoked response by sensory stimulation, Second, a battery of tests studying various spinal functions in the lower limbs has been applied. Motor cortex is more excitable in Parkinsonian patients and the initial phase of inhibition following sensory conditioning is reduced. These changes have no good correlation with intensity of the signs assessed by Webster’s scale. At the spinal level, excitability of the motoneuron pool, presynaptic inhibi-[ion (measured by the vibratory inhibition) and recurrent inhibition are normal. Peciprocai inhibition mediated by the la interneuron is more marked while non reciprocal inhibition, utilizing the lb interneuron, is clearly reduced or even replaced by facilitation. The departures from normal values are nicely correlated with rigidity intensity (r=0.69 and 0,79 respectively). The conclusions of this comprehensive electrophysiological study are: (I) rigidity can be interpreted by a spinal mechanism i.e. the reduction of non-reciprocal inhibition which no more counterbalances excitatory afferents (Delwaide et al., 1991); (2) changes in both la and lb interneuron excitability indicate that reticuiospinai pathways are involved in pathophysiology of rigidity; (3) increased excitability of the corticospinal tract may be viewed as a compansatory mechanism: execution of a movement is no more correctly assisted by spinal mechanisms and requires a larger contribution of the pyramidal tract.
Palatal Tremor G, Deuschl. Neuroiogische Klinik und Polikiinik UniversiW Freiburg, Hansastc 9, 7800 Freiburg, Germany Palatal tremor is rare but important for the understanding of the mechanisms underlying rhythmic movement disorders. Recent evidence suggests two types of palatal tremor. Symptomatic palatal tremor (SPT) develops following a brainstemicerebeliar disorder, manifests with rhythmic movements of the palatale and various other brainstem and extremity muscles, and is associated with MRI-evidence for olivary pseudo-hypertrophy. Essential palatal tremor (EPT) manifests with a rhythmic earclick and palatai movements but without any hints of olivary abnormalities. SPT and EPT differ in several pathophysiologic aspects. The presumed oscillator of SPT is less influenced by wakefulness than in EPT. There is a generalized remote effect of SPT but not of EPT. Motor adaption of brainstem and arm muscle functions is affected in SPT but not in EPT. PET results suggest abnormalities of the cerebellum in SPT but not in EPT. In conclusion, these findings demonstrate profound clinica! and pathophysiological differences of these two conditions. Different oscillators can be assumed for them. The mechanisms underlying SPT might share similarities with those of postural tremors in genera!,
Task-Dependent
Modulation af Spinai ~~~~~~~~
V Dietz. Swiss Paraplegic Centre Balgnst, ForchstraRe 340, 8008 ZiIrich. Switzerland Holding the body’s centre of gravity steady represents the crucial variable for the stabilization of posture in upright stance in man. From two novel experimental approaches it becomes obvious, that force-dependent receptors are required. In addition to the weil known systems involved in sway stabilization, for equilibrium control. The one approach concerns the control of bilateral leg muscle activation during stance. Standing on a treadmill with split belts unilateral or bilateral leg displacements were induced. An unilateral displacement induced a biiaterai EMG response. During bilateral displacements the EMG activity was linearly summed or subtracted, depending on whether the legs were displaced in the same or opposite directions. In such a functional motor task, both legs act in a cooperative manner: each limb affects the strength of muscle activation and the time space behaviour of the other. This inter-limb coordination is suggested to be mediated by spinal interneuronal circuits, which are themselves under supraspinal (e.g. cerebellar) control. The other approach concerns the modulation of postural reflexes under simulated “microgravity” in water immersion. An approximately linear relationship was found between contact forces and impulse directed EMG response amplitudes in the leg muscles, Out of water loading of the subjects resulted in no further increase of the response amplitude. It was concluded that the function of proprioceptive reflexes involved in the stabilization of posture depends on the presence of contact forces opposing gravity. Extensor load receptors are thought to signal changes of the projection of body’s centre of mass with respect to the feet. The interaction of the afferent input from these receptors with the other systems involved in postural control is not yet fully understood.
Measuring Residual Mator Functions efter Spin Milan R. Dimitrijevic. Bay/or College oi Medicine, Div. of Restorative Neurology and Human Neurobiology. One Baylor Plaza. Houston, lX17030, USA We shall describe the clinical neurophysiologicai methods for the measurement of residual and altered spinal cord functions in humanswith neurological findings for complete and incomplete spinal cord lesions. Characieristics features of spinal motor nuclei activity will be given together with the kind of related segmental and suprasegmental mechanisms. We shall illustrate the functional organization of spinal neurons and interneurons when they are only under brain influence (discomplete lesion [l]) or brain influence and partial brain motor controi (incomplete lesion ]2]). The summary of neurobiology of upper motor neuron (UMNJ paralysis and paresis contributes to the development and clinical use of neurophysiological rmethods for the assessment of UMN functions of the intact and diseased nervous system. [l]
Sherwood, A.M., Dimrtrijevic, M.R.. McKay, WB. Evidence of subclinical brain influence in clinically complete spinal ccrd injury: discomplete SCI. J. Neural. Sci., 110: 90-98. 1992.
pathalogy.
In GBS patients
distal latency in median, ulnar
and common peroneal nerves was prolonged while mean motor NC was decreased to 44.12 + 13.7, 46.18 i 17.02 b33.12 jL 10.67 m/set respectively. Thirty five patients (30 M, 5 F) had Arsenic neuropathy. EMG was neurogenic in 80% cases while sural nerve action potential was absent in 14 (40%) instances. Other important categories of PN included hereditary neuropathies (5.3%). nutritional neuropathies (3.8%). collagen vascular disease (5.7%) and post vaccinal neuropathy (3.6%). Clinical and eiectrophysiological details will be discussed and campared with published data from other tropical countries.
otentials in Alzheimer
Diseases
G. Comi. Dept. of Neuroiog~ Scientific Institute U.S. Raffaeale, University of Milan, Via 0lgeOina 60, 211132 Milano, ltalia in this review we will focus on the clinical value of long latency cognitive event-related potentials (ERPs) in dementia of the Alzheimer type (DAT). Most clinical studies on the ERPs have been on the P300 component which has been shown to reflect the fundamental cognitive events, involving stimulus evaluation and immediate memory. There is a general agreement between laboratories that the !atency of P300 is increased and the amplitude is decreased in DAT patients compared to normal controls and patients with other psychiatric conditions, when the comparison is made between groups. What is controversial is the utility of the test as diagnostic procedure. The sensitivity vary from 7% to 83% across reports; differences between the studies in terms of experimental task, methods of analysis and selection of patients and controls contribute to the discrepancy in results. Most clinical studies utilized only a few recording sites, some recent studies suggest that topographic mapping will result in an increase of sensitivity and specificity of P300. DAT is an almost invariable accompaniment of ageing in Down’s syndrome. In Down’s patients P300 latency is increased and amplitude is reduced and the effects of age on P300 are anticipated of about 20 years compared to health population, We recently found that topographic distribution of P3OO is frequently abnormal in Down’s syndrome; the development of dementia in these patients is accompanied by a significant increase of P300 iatency.
l?J. Delwaide. University oftiege, I, 4000 Li&ge, Beigium
H6pital de la Citadeile, Ed. du 12” de Ligne
The neurophysiological mechanisms underlying Parkinsonian rigidity are far from clear. It has first been proposed that changes in gamma innervation could explain Parkrnsonian stiffness but later, an alternative explanation has proposed a hyperactivity in a long loop reflex pathway relaying in the motor cortex. However, the question remains controversial and justifies further studies. We have conducted electrophysiological studies on 70 Parkinsonian patients (39 males; 31 females) at various stages and 49 age-matched controls. We first used magnetic transcranial stimulation to determine the activation threshold and the conditioning of the evoked response by sensory stimulation, Second, a battery of tests studying various spinal functions in the lower limbs has been applied. Motor cortex is more excitable in Parkinsonian patients and the initial phase of inhibition following sensory conditioning is reduced. These changes have no good correlation with intensity of the signs assessed by Webster’s scale. At the spinal level, excitability of the motoneuron pool, presynaptic inhibi-[ion (measured by the vibratory inhibition) and recurrent inhibition are normal. Peciprocai inhibition mediated by the la interneuron is more marked while non reciprocal inhibition, utilizing the lb interneuron, is clearly reduced or even replaced by facilitation. The departures from normal values are nicely correlated with rigidity intensity (r=0.69 and 0,79 respectively). The conclusions of this comprehensive electrophysiological study are: (I) rigidity can be interpreted by a spinal mechanism i.e. the reduction of non-reciprocal inhibition which no more counterbalances excitatory afferents (Delwaide et al., 1991); (2) changes in both la and lb interneuron excitability indicate that reticuiospinai pathways are involved in pathophysiology of rigidity; (3) increased excitability of the corticospinal tract may be viewed as a compansatory mechanism: execution of a movement is no more correctly assisted by spinal mechanisms and requires a larger contribution of the pyramidal tract.
Palatal Tremor G, Deuschl. Neuroiogische Klinik und Polikiinik UniversiW Freiburg, Hansastc 9, 7800 Freiburg, Germany Palatal tremor is rare but important for the understanding of the mechanisms underlying rhythmic movement disorders. Recent evidence suggests two types of palatal tremor. Symptomatic palatal tremor (SPT) develops following a brainstemicerebeliar disorder, manifests with rhythmic movements of the palatale and various other brainstem and extremity muscles, and is associated with MRI-evidence for olivary pseudo-hypertrophy. Essential palatal tremor (EPT) manifests with a rhythmic earclick and palatai movements but without any hints of olivary abnormalities. SPT and EPT differ in several pathophysiologic aspects. The presumed oscillator of SPT is less influenced by wakefulness than in EPT. There is a generalized remote effect of SPT but not of EPT. Motor adaption of brainstem and arm muscle functions is affected in SPT but not in EPT. PET results suggest abnormalities of the cerebellum in SPT but not in EPT. In conclusion, these findings demonstrate profound clinica! and pathophysiological differences of these two conditions. Different oscillators can be assumed for them. The mechanisms underlying SPT might share similarities with those of postural tremors in genera!,
Task-Dependent
Modulation af Spinai ~~~~~~~~
V Dietz. Swiss Paraplegic Centre Balgnst, ForchstraRe 340, 8008 ZiIrich. Switzerland Holding the body’s centre of gravity steady represents the crucial variable for the stabilization of posture in upright stance in man. From two novel experimental approaches it becomes obvious, that force-dependent receptors are required. In addition to the weil known systems involved in sway stabilization, for equilibrium control. The one approach concerns the control of bilateral leg muscle activation during stance. Standing on a treadmill with split belts unilateral or bilateral leg displacements were induced. An unilateral displacement induced a biiaterai EMG response. During bilateral displacements the EMG activity was linearly summed or subtracted, depending on whether the legs were displaced in the same or opposite directions. In such a functional motor task, both legs act in a cooperative manner: each limb affects the strength of muscle activation and the time space behaviour of the other. This inter-limb coordination is suggested to be mediated by spinal interneuronal circuits, which are themselves under supraspinal (e.g. cerebellar) control. The other approach concerns the modulation of postural reflexes under simulated “microgravity” in water immersion. An approximately linear relationship was found between contact forces and impulse directed EMG response amplitudes in the leg muscles, Out of water loading of the subjects resulted in no further increase of the response amplitude. It was concluded that the function of proprioceptive reflexes involved in the stabilization of posture depends on the presence of contact forces opposing gravity. Extensor load receptors are thought to signal changes of the projection of body’s centre of mass with respect to the feet. The interaction of the afferent input from these receptors with the other systems involved in postural control is not yet fully understood.
Measuring Residual Mator Functions efter Spin Milan R. Dimitrijevic. Bay/or College oi Medicine, Div. of Restorative Neurology and Human Neurobiology. One Baylor Plaza. Houston, lX17030, USA We shall describe the clinical neurophysiologicai methods for the measurement of residual and altered spinal cord functions in humanswith neurological findings for complete and incomplete spinal cord lesions. Characieristics features of spinal motor nuclei activity will be given together with the kind of related segmental and suprasegmental mechanisms. We shall illustrate the functional organization of spinal neurons and interneurons when they are only under brain influence (discomplete lesion [l]) or brain influence and partial brain motor controi (incomplete lesion ]2]). The summary of neurobiology of upper motor neuron (UMNJ paralysis and paresis contributes to the development and clinical use of neurophysiological rmethods for the assessment of UMN functions of the intact and diseased nervous system. [l]
Sherwood, A.M., Dimrtrijevic, M.R.. McKay, WB. Evidence of subclinical brain influence in clinically complete spinal ccrd injury: discomplete SCI. J. Neural. Sci., 110: 90-98. 1992.