- Email: [email protected]
Computerized chromatic visual field analysis in M.S.
56P
Society
100 units. The following parameters of SSR have been considered: latency at the onset (hand and foot), hand-foot difference in latency, peak-to-peak amplitude (hand and foot), ratio in amplitude between hand and foot responses. The results obtained in baseline conditions and after Bo-NT therapy are reported in the following table: (Baseline, after Bo-NT, Student’s t test) latency (hand) (I .3 + 0.2 ms, 1.5 + 0.6 ms, N.S.), latency (foot) (2.1 + 0.3 ms, 2 + 0.3 ms, N.S.), latency (hand/foot difference) (0.7 + 0.3 ms, 0.7 + 0.3 ms, N.S.), amplitude (hand) (0.9 + 0.7 mV, 1.3 + 0.9 mV, N.S.), amplitude (foot) (0.7 + 1.1 mV, 0.7 + 1 mV, N.S.), amplitude (hand/foot ratio) (3.1 + 2.9, 3.5 + 3.3, N.S.). In conclusion Bo-NT therapy did not induce significant alterations in sympathetic skin response. 5.
Electrophysiological studies in mild idiopathic carpal tunnel syndrome: follow-up. - P. Girlanda, A. Quartarone, G. Picciolo, V. Macaione, S. Sinicropi, C. Nicolosi, C. Messina (Institute of Neurological and Neurosurgical Sciences, University of Messina, Italy)
We have already used an electrophysiological protocol including the assessment of the ortbodromic sensory conduction velocity of median nerve along the carpal tunnel, the comparison of median and ulnar sensory conduction between ring linger and wrist, the short segment incremental median sensory nerve conduction across the carpal tunnel recording from the 3rd digit (‘inching test’), and the study of the refractory period of transmission (RPT) in 20 patients with mild CTS (37 symptomatic hands) with a distal motor latency of median nerve lower than 4 ms and in 20 control subjects. Combining the different techniques we could reach an overall sensitivity of 83%. We tested the patients again 2 years after the first examination to obtain history and clinical updating and electrophysiological data including distal motor latency (MAP-DL) of median nerve and a sensory conduction study between the 3rd finger and wrist (SCV-3rdF-W). Sixteen patients (30 symptomatic hands) underwent the follow-up examination. Three patients had been treated surgically with complete recovery and 8 hands had received local injection of steroids with transient benefit; 33% of hands which were abnormal at the first electrophysiological study showed a MAP-DL higher than 4 ms at the follow-up examination and 70% of hands revealed abnormal SCV-3rdF-W. No hand was normal at the first control revealed electrophysiological abnormalities at the follow-up. Also statistical comparisons concerning clinical score and electrophysiological findings showed that the group of hands positive at the first electrophysiological control presented a clear-cut worsening at the follow-up while the group of hands negative at the first examination remained unmodified. Therefore the electrodiagnostic protocol that we used in mild CTS revealed not only a high sensitivity but also a good specificity. 6.
Electrophysiological responses deprivation: an in vitro study. Calahresi (Neurological Clinic
of basal ganglia neurons to 02 - G. Bernardi, N.B. Mercuri, P. University Tor Vergata, Rome)
In this work we employed intracellular electrophysiological techniques to examine the effects of hypoxia on rat mesencephalic dopaminergic and striatal medium spiny cells maintained in vitro. Hypoxia was caused by changing the perfusing solution saturated with 95% 02/S% CO2 with one gassed with N2 95%/CO2 5%. Both mesencephalic and striatal cells readily responded to the hypoxic stimulus within l-2 min, but the membrane changes were different. In fact, it was observed that the dopaminergic cells were mainly hyperpolarized while the striatal neurons were depolarized. The two responses were associated with a decrease in apparent input resistance. Under voltage clamp conditions, the membrane hyperpolatization of the dopaminergic neurons was due to an outward current while the membrane depolarzation of striatal cells was due to an inward current. The cellular responses to hypoxia in the dopaminergic cells were largely mediated by an increase in potassium conductance. On the contrary the hypoxia-
Proceedings induced depolarization of striatal cells was largely mediated by an influx of sodium ions as a consequence of the blockade of the Na+/K+ ATP-dependent pump and the opening of sodium channels. By using antagonists for the excitatory amino acids (APV, CNQX) it was observed that neither the membrane hyperpolarization or the membrane depolarization were dependent on the release of endogenous amino acids. The dopaminergic cells were more resistant to hypoxia than the striatal neurons. This is in accordance with clinical evidence showing the particular vulnerability of striatal cells to hypoxia and ischemia. 7.
Execution of differently programmed motor programmed motor sequences. - A. Curra, M. Modugno, R. Agosino, G.W. Manfredi, N. Accornero, A. Berardelli (Neurological Department, University “La Sapienza” of Rome)
Parkinsonian patients are slower than normal subjects in executing sequential arm movements and show a progressive slowing as the sequence is completed. In this study the utilization of advance information to perform motor sequences has been studied in 10 normal and 3 parkinsonian subjects. The kinematics of the hand was monitored using a TV image processor which detected the position of a reflective marker placed on the second finger of the subject (ELITE System, BTS). Subjects performed sequences following visual targets on a screen. In the KNOWN sequences all the targets were displayed on the screen before a verbal starting signal (pre-programmed). In the UNKNOWN sequences the targets were displayed consecutively after the starting signal (not-pre-programmed). (1) Patients were slower than controls in executing both UNKNOWN and KNOWN sequences; (2) both groups were faster in performing the KNOWN sequences, but MT reduction was significantly shorter in patients; (3) a progressive slowing of MT as the sequences were completed, was present in both groups during the UNKNOWN task, but only in the patients during the KNOWN task. These results support the hypothesis that parkinsonians have more difficulties in executing movements that need to be programmed in advance than stimulus-response movements. 8.
Coherence and power spectral analysis in simple and complex finger movements. - P. Manganotti, C. Toro, L. Leocani, P. Zhuang, M. Hallett (NfH Bethesda, MD)
The sensorimotor cortical activation during movement was studied electrophysiologically in 7 right handed subjects using the coherence and power spectral analysis techniques. The motor task involved four finger movement sequences of increasing complexity, Movements were metronome paced at a rate of 2 Hz. Sequences were performed in 2 trials of 120 linger movements each. Coherence and power spectral analysis were computed within alpha and beta frequency bands for 29 scalp EEG channels. Both hands showed coherence increase and power decrease over central and frontal scalp electrodes within and across hemispheres during finger sequences compared to rest. Also coherence decreases were observed across posterior scalp electrodes. In both frequency bands, coherence increases and the power decreases were greater for sequences of higher complexity. These findings suggest that more complex tasks require higher levels of local cortical activation and the establishment of broader functional connections over the sensorimotor areas. 9.
Computerized chromatic visual field analysis in M.S. Accorneroa S. Rinalduzzi”, M. Filippp’, E. Millefiorini”, Capitaniob,’ G.C. Filligoib (aDipartimento di Scienze rologiche. bDip Infocom Universita “La Sapienza” Rome)
- N. L. Neu-
A software procedure running on a PC with standard peripherals has been developed in order to define chromatic perception extension in the central visual field (40 X 24). Accuracy and rapidity appear the major features. Sensitivity of the test is also high since mild chromatic visual
Society defect can be surely classified when subject is unaware of it. Detection of mild chromatic impairment appears crucial for the early diagnosis in many neurological and ophthalmic diseases. A pilot study on MS patients shows meaningful statistical sensitivity of this test against standard ‘luminance’ visual field analysis.
10. Platformless posturography. - N. Accornero, M. Capozza, S. Rlnalduzzi, G.W. Manfredi @ipartimento di Scienze Neurologiche Universiti ‘La Sapienza’ Rome) Posturography traditionally is attained using electronic devices that locate the projection of the body barycentre on a force platform and analyze its sway during a given period of time. Much useful information is easily available in this way but some compensation movements of the body that keep the barycentre are still lost, and further, the amplitude of the recorded sway depends strictly upon the standing area covered by the feet. A different approach utilizes accelerometers or position markers strategically located on body segments. Virtual reality electromagnetic tracking devices am now commercially available at moderate cost providing good spatial and temporal resolution and easy handling. In this paper we describe some of the results obtained with a two points positions tracker (head and hip) in normal people performing the Romberg test that indicate different standing control in younger and older subjects.
11. Effect of transcranial magnetic stimulation on the execution of sequential finger movements. - (B. Mercuri, S. Rona, L. Vacca, M. Inghillerl, G.W. Manfredi, A. Berardelli) Magnetic stimulation of motor cortical areas can delay the execution of voluntary movements of the upper limbs. In this study we have analyzed the effect of magnetic stimuli, delivered before movement onset, on the execution of sequential finger movements. Magnetic stimuli were delivered through a large circular coil placed at the vertex (diffuse stimulus), or through a small circular coil placed over the left primary motor cortex (focal stimulus), at an intensity of 1.5 times the motor threshold for the activation of controlateral small hand muscles. Subjects were asked to perform rapid sequential finger movements, either with one hand alone or with both hands simultaneously. ‘Diffuse’ magnetic stimulation delayed the onset of all movements by about 300 ms, without altering movement duration. ‘Focal’ stimulation caused a shorter delay of bimanual and contralateral movements while not affecting ipsilateral hand movements when tested alone.
12. Prognostic value of transcranial magnetic stimulation and SEP in stroke. - M. Turazzini, R. Del Colle, R. Bassi, M. Silvestri, G. Zanettea (Division of Neurology - Legnago. aInstitute of Neurology, University Verona) The aim of this study was to evaluate the role of neurophysiological parameters in predicting functional recovery in patient with stroke. Ten patients with radiologically confirmed stroke and varying degrees of hemiparesis were studied using somatosensory evoked potentials by stimulation of the posterior tibial nerve and transcranial magnetic stimulation. The SEP and MEP were recorded within the first week, 4 week and 9 months after stroke onset. In the acute period, cortical SEP were. present in 3 hemiparetic and 1 hemiplegic patients; MEP could be detected only in the hemiplegic patient, The motor response was absent in the other 9 patients. In the first follow-up, SEP appear in 3 patients and MEP in 4. These parameters were correlated with functional recovery (middle and good). In the last control, no significant differences were observed. In conclusion patients with the presence of neurophysiological responses in the acute period or in the first control showed a significant clinical recovery compared to the others. The use of the SEP and MEP compared with stroke degree of recovery had value in predicting the outcome of disease.
Proceedings
5lP
13. Non-invasive mapping of motor cortical representations of the upper limb muscles through transcranial magnetic stimulation. - G. Zanette, M. Tinazzi, A. Di Summa, A. Polo, G. Bona@ P. Manganotti, A. Fiaschi (Dipartimento di Scienze Neurologiche e della Visione, Sezione di Neurologia, Verona, Italy) Mapping of human motor cortex by transcranial magnetic stimulation seems to provide a contribution to the knowledge of adaptive and reorganization processes of the CNS. We mapped the cortical representations of the opponens pollicis, flexor carpi radialis, biceps brachialis and deltoid muscles in 15 healthy subjects evaluating both hemispheres in one recording session. A grid of positions 1 cm apart with reference to Cz was marked on an elastic cuff; 3 MEPs to focal magnetic pulses produced in each muscle at each scalp position were averaged off line and expressed as a percentage of the CAMP (% M). The following parameters of the cortical maps were evaluated: number of excitable scalp positions (area); the optimal scalp position; volume; the % M amplitude distribution; the lowest threshold stimulation zone; asymmetry. No % MS were evoked from the middle scalp positions. Cortical maps for distal muscles were larger if compared to those for proximal muscles and were represented more in the left hemisphere; they can extend for a few centimeters in front and behind the coronal line passing through Cz, with optimal position I cm in front and 6 cm lateral to it. Proximal muscles were more easily excitable l-2 cm medial to this position.
14. Mechanisms of motor cortex excitability modulation after exercise. - C. Bonato, G. Zanette, M. Tinazzi, A. Polo, LG. Bongiovanni, P. Manganotti, A. Di Summa, A. Fiaschi (Dipartimento di Scienze Neurologiche e della Visione, Sezione di Neurologia, Verona, Italy) We recently observed an immediate and long-lasting decrease in motor evoked potential (MEP) amplitude to transcranial magnetic stimulation (TMS) after rapid repetitive abduction-adduction movements of the thumb. To better deIine possible mechanisms involved in this phenomenon we verified: (1) its relation to spindle muscle firing evaluated by a vibratory stimulation (150 Hz applied for 1 min at the right thenar eminence in 5 subjects) which did not produce any modification in MEP amplitude; (2) its diffusion to nontarget muscles (10 subjects): no effect at ipsilateral triceps brachialis and deltoid muscles; inconstant decrease in MEP amplitude at ipsilateral biceps brachialis muscle; significant MEP amplitude decrease at contralateral opponens pollicis muscle which started at the post-exercise 5th minute, reached its 30-35% mean maximal value and recovered within 35 min. We conclude that post-exercise motor cortex excitability modulation does not depend on propioceptive afferent input and it is target-specific, if we exclude its delayed diffusion to the controlateral homologous cortical area which strongly suggests an interhemispheric transfer of plasticity. The immediate MEP amplitude decrease for the target muscle may depend on neurotransmitter depletion in the motor cortical area activated during the exercise.
15. Effect of stimulus rate on the cortical posterior tibia1 nerve SEPs: a topographic study. - M. Tinazzi, G. Zanette, C. Bonato, A. Polo, A. Fiaschi, F. Mauguierea (Department of Neurological and Visual Sciences, Verona, Italy. aFunctional Neurology and Epileptology Department, Neurologic, Lyon, France) We performed topographic mapping of somatosensory evoked potentials to posterior tibia1 nerve stimulation delivered at 2, 5 and 7.5 Hz in 15 healthy subjects. P37 was attenuated significantly at 5 and 7.5 Hz and N50 component attenuated only at 5 Hz, its amplitude remaining stable for further increases of stimulus frequency. Frontal N37 and P50
Society
100 units. The following parameters of SSR have been considered: latency at the onset (hand and foot), hand-foot difference in latency, peak-to-peak amplitude (hand and foot), ratio in amplitude between hand and foot responses. The results obtained in baseline conditions and after Bo-NT therapy are reported in the following table: (Baseline, after Bo-NT, Student’s t test) latency (hand) (I .3 + 0.2 ms, 1.5 + 0.6 ms, N.S.), latency (foot) (2.1 + 0.3 ms, 2 + 0.3 ms, N.S.), latency (hand/foot difference) (0.7 + 0.3 ms, 0.7 + 0.3 ms, N.S.), amplitude (hand) (0.9 + 0.7 mV, 1.3 + 0.9 mV, N.S.), amplitude (foot) (0.7 + 1.1 mV, 0.7 + 1 mV, N.S.), amplitude (hand/foot ratio) (3.1 + 2.9, 3.5 + 3.3, N.S.). In conclusion Bo-NT therapy did not induce significant alterations in sympathetic skin response. 5.
Electrophysiological studies in mild idiopathic carpal tunnel syndrome: follow-up. - P. Girlanda, A. Quartarone, G. Picciolo, V. Macaione, S. Sinicropi, C. Nicolosi, C. Messina (Institute of Neurological and Neurosurgical Sciences, University of Messina, Italy)
We have already used an electrophysiological protocol including the assessment of the ortbodromic sensory conduction velocity of median nerve along the carpal tunnel, the comparison of median and ulnar sensory conduction between ring linger and wrist, the short segment incremental median sensory nerve conduction across the carpal tunnel recording from the 3rd digit (‘inching test’), and the study of the refractory period of transmission (RPT) in 20 patients with mild CTS (37 symptomatic hands) with a distal motor latency of median nerve lower than 4 ms and in 20 control subjects. Combining the different techniques we could reach an overall sensitivity of 83%. We tested the patients again 2 years after the first examination to obtain history and clinical updating and electrophysiological data including distal motor latency (MAP-DL) of median nerve and a sensory conduction study between the 3rd finger and wrist (SCV-3rdF-W). Sixteen patients (30 symptomatic hands) underwent the follow-up examination. Three patients had been treated surgically with complete recovery and 8 hands had received local injection of steroids with transient benefit; 33% of hands which were abnormal at the first electrophysiological study showed a MAP-DL higher than 4 ms at the follow-up examination and 70% of hands revealed abnormal SCV-3rdF-W. No hand was normal at the first control revealed electrophysiological abnormalities at the follow-up. Also statistical comparisons concerning clinical score and electrophysiological findings showed that the group of hands positive at the first electrophysiological control presented a clear-cut worsening at the follow-up while the group of hands negative at the first examination remained unmodified. Therefore the electrodiagnostic protocol that we used in mild CTS revealed not only a high sensitivity but also a good specificity. 6.
Electrophysiological responses deprivation: an in vitro study. Calahresi (Neurological Clinic
of basal ganglia neurons to 02 - G. Bernardi, N.B. Mercuri, P. University Tor Vergata, Rome)
In this work we employed intracellular electrophysiological techniques to examine the effects of hypoxia on rat mesencephalic dopaminergic and striatal medium spiny cells maintained in vitro. Hypoxia was caused by changing the perfusing solution saturated with 95% 02/S% CO2 with one gassed with N2 95%/CO2 5%. Both mesencephalic and striatal cells readily responded to the hypoxic stimulus within l-2 min, but the membrane changes were different. In fact, it was observed that the dopaminergic cells were mainly hyperpolarized while the striatal neurons were depolarized. The two responses were associated with a decrease in apparent input resistance. Under voltage clamp conditions, the membrane hyperpolatization of the dopaminergic neurons was due to an outward current while the membrane depolarzation of striatal cells was due to an inward current. The cellular responses to hypoxia in the dopaminergic cells were largely mediated by an increase in potassium conductance. On the contrary the hypoxia-
Proceedings induced depolarization of striatal cells was largely mediated by an influx of sodium ions as a consequence of the blockade of the Na+/K+ ATP-dependent pump and the opening of sodium channels. By using antagonists for the excitatory amino acids (APV, CNQX) it was observed that neither the membrane hyperpolarization or the membrane depolarization were dependent on the release of endogenous amino acids. The dopaminergic cells were more resistant to hypoxia than the striatal neurons. This is in accordance with clinical evidence showing the particular vulnerability of striatal cells to hypoxia and ischemia. 7.
Execution of differently programmed motor programmed motor sequences. - A. Curra, M. Modugno, R. Agosino, G.W. Manfredi, N. Accornero, A. Berardelli (Neurological Department, University “La Sapienza” of Rome)
Parkinsonian patients are slower than normal subjects in executing sequential arm movements and show a progressive slowing as the sequence is completed. In this study the utilization of advance information to perform motor sequences has been studied in 10 normal and 3 parkinsonian subjects. The kinematics of the hand was monitored using a TV image processor which detected the position of a reflective marker placed on the second finger of the subject (ELITE System, BTS). Subjects performed sequences following visual targets on a screen. In the KNOWN sequences all the targets were displayed on the screen before a verbal starting signal (pre-programmed). In the UNKNOWN sequences the targets were displayed consecutively after the starting signal (not-pre-programmed). (1) Patients were slower than controls in executing both UNKNOWN and KNOWN sequences; (2) both groups were faster in performing the KNOWN sequences, but MT reduction was significantly shorter in patients; (3) a progressive slowing of MT as the sequences were completed, was present in both groups during the UNKNOWN task, but only in the patients during the KNOWN task. These results support the hypothesis that parkinsonians have more difficulties in executing movements that need to be programmed in advance than stimulus-response movements. 8.
Coherence and power spectral analysis in simple and complex finger movements. - P. Manganotti, C. Toro, L. Leocani, P. Zhuang, M. Hallett (NfH Bethesda, MD)
The sensorimotor cortical activation during movement was studied electrophysiologically in 7 right handed subjects using the coherence and power spectral analysis techniques. The motor task involved four finger movement sequences of increasing complexity, Movements were metronome paced at a rate of 2 Hz. Sequences were performed in 2 trials of 120 linger movements each. Coherence and power spectral analysis were computed within alpha and beta frequency bands for 29 scalp EEG channels. Both hands showed coherence increase and power decrease over central and frontal scalp electrodes within and across hemispheres during finger sequences compared to rest. Also coherence decreases were observed across posterior scalp electrodes. In both frequency bands, coherence increases and the power decreases were greater for sequences of higher complexity. These findings suggest that more complex tasks require higher levels of local cortical activation and the establishment of broader functional connections over the sensorimotor areas. 9.
Computerized chromatic visual field analysis in M.S. Accorneroa S. Rinalduzzi”, M. Filippp’, E. Millefiorini”, Capitaniob,’ G.C. Filligoib (aDipartimento di Scienze rologiche. bDip Infocom Universita “La Sapienza” Rome)
- N. L. Neu-
A software procedure running on a PC with standard peripherals has been developed in order to define chromatic perception extension in the central visual field (40 X 24). Accuracy and rapidity appear the major features. Sensitivity of the test is also high since mild chromatic visual
Society defect can be surely classified when subject is unaware of it. Detection of mild chromatic impairment appears crucial for the early diagnosis in many neurological and ophthalmic diseases. A pilot study on MS patients shows meaningful statistical sensitivity of this test against standard ‘luminance’ visual field analysis.
10. Platformless posturography. - N. Accornero, M. Capozza, S. Rlnalduzzi, G.W. Manfredi @ipartimento di Scienze Neurologiche Universiti ‘La Sapienza’ Rome) Posturography traditionally is attained using electronic devices that locate the projection of the body barycentre on a force platform and analyze its sway during a given period of time. Much useful information is easily available in this way but some compensation movements of the body that keep the barycentre are still lost, and further, the amplitude of the recorded sway depends strictly upon the standing area covered by the feet. A different approach utilizes accelerometers or position markers strategically located on body segments. Virtual reality electromagnetic tracking devices am now commercially available at moderate cost providing good spatial and temporal resolution and easy handling. In this paper we describe some of the results obtained with a two points positions tracker (head and hip) in normal people performing the Romberg test that indicate different standing control in younger and older subjects.
11. Effect of transcranial magnetic stimulation on the execution of sequential finger movements. - (B. Mercuri, S. Rona, L. Vacca, M. Inghillerl, G.W. Manfredi, A. Berardelli) Magnetic stimulation of motor cortical areas can delay the execution of voluntary movements of the upper limbs. In this study we have analyzed the effect of magnetic stimuli, delivered before movement onset, on the execution of sequential finger movements. Magnetic stimuli were delivered through a large circular coil placed at the vertex (diffuse stimulus), or through a small circular coil placed over the left primary motor cortex (focal stimulus), at an intensity of 1.5 times the motor threshold for the activation of controlateral small hand muscles. Subjects were asked to perform rapid sequential finger movements, either with one hand alone or with both hands simultaneously. ‘Diffuse’ magnetic stimulation delayed the onset of all movements by about 300 ms, without altering movement duration. ‘Focal’ stimulation caused a shorter delay of bimanual and contralateral movements while not affecting ipsilateral hand movements when tested alone.
12. Prognostic value of transcranial magnetic stimulation and SEP in stroke. - M. Turazzini, R. Del Colle, R. Bassi, M. Silvestri, G. Zanettea (Division of Neurology - Legnago. aInstitute of Neurology, University Verona) The aim of this study was to evaluate the role of neurophysiological parameters in predicting functional recovery in patient with stroke. Ten patients with radiologically confirmed stroke and varying degrees of hemiparesis were studied using somatosensory evoked potentials by stimulation of the posterior tibial nerve and transcranial magnetic stimulation. The SEP and MEP were recorded within the first week, 4 week and 9 months after stroke onset. In the acute period, cortical SEP were. present in 3 hemiparetic and 1 hemiplegic patients; MEP could be detected only in the hemiplegic patient, The motor response was absent in the other 9 patients. In the first follow-up, SEP appear in 3 patients and MEP in 4. These parameters were correlated with functional recovery (middle and good). In the last control, no significant differences were observed. In conclusion patients with the presence of neurophysiological responses in the acute period or in the first control showed a significant clinical recovery compared to the others. The use of the SEP and MEP compared with stroke degree of recovery had value in predicting the outcome of disease.
Proceedings
5lP
13. Non-invasive mapping of motor cortical representations of the upper limb muscles through transcranial magnetic stimulation. - G. Zanette, M. Tinazzi, A. Di Summa, A. Polo, G. Bona@ P. Manganotti, A. Fiaschi (Dipartimento di Scienze Neurologiche e della Visione, Sezione di Neurologia, Verona, Italy) Mapping of human motor cortex by transcranial magnetic stimulation seems to provide a contribution to the knowledge of adaptive and reorganization processes of the CNS. We mapped the cortical representations of the opponens pollicis, flexor carpi radialis, biceps brachialis and deltoid muscles in 15 healthy subjects evaluating both hemispheres in one recording session. A grid of positions 1 cm apart with reference to Cz was marked on an elastic cuff; 3 MEPs to focal magnetic pulses produced in each muscle at each scalp position were averaged off line and expressed as a percentage of the CAMP (% M). The following parameters of the cortical maps were evaluated: number of excitable scalp positions (area); the optimal scalp position; volume; the % M amplitude distribution; the lowest threshold stimulation zone; asymmetry. No % MS were evoked from the middle scalp positions. Cortical maps for distal muscles were larger if compared to those for proximal muscles and were represented more in the left hemisphere; they can extend for a few centimeters in front and behind the coronal line passing through Cz, with optimal position I cm in front and 6 cm lateral to it. Proximal muscles were more easily excitable l-2 cm medial to this position.
14. Mechanisms of motor cortex excitability modulation after exercise. - C. Bonato, G. Zanette, M. Tinazzi, A. Polo, LG. Bongiovanni, P. Manganotti, A. Di Summa, A. Fiaschi (Dipartimento di Scienze Neurologiche e della Visione, Sezione di Neurologia, Verona, Italy) We recently observed an immediate and long-lasting decrease in motor evoked potential (MEP) amplitude to transcranial magnetic stimulation (TMS) after rapid repetitive abduction-adduction movements of the thumb. To better deIine possible mechanisms involved in this phenomenon we verified: (1) its relation to spindle muscle firing evaluated by a vibratory stimulation (150 Hz applied for 1 min at the right thenar eminence in 5 subjects) which did not produce any modification in MEP amplitude; (2) its diffusion to nontarget muscles (10 subjects): no effect at ipsilateral triceps brachialis and deltoid muscles; inconstant decrease in MEP amplitude at ipsilateral biceps brachialis muscle; significant MEP amplitude decrease at contralateral opponens pollicis muscle which started at the post-exercise 5th minute, reached its 30-35% mean maximal value and recovered within 35 min. We conclude that post-exercise motor cortex excitability modulation does not depend on propioceptive afferent input and it is target-specific, if we exclude its delayed diffusion to the controlateral homologous cortical area which strongly suggests an interhemispheric transfer of plasticity. The immediate MEP amplitude decrease for the target muscle may depend on neurotransmitter depletion in the motor cortical area activated during the exercise.
15. Effect of stimulus rate on the cortical posterior tibia1 nerve SEPs: a topographic study. - M. Tinazzi, G. Zanette, C. Bonato, A. Polo, A. Fiaschi, F. Mauguierea (Department of Neurological and Visual Sciences, Verona, Italy. aFunctional Neurology and Epileptology Department, Neurologic, Lyon, France) We performed topographic mapping of somatosensory evoked potentials to posterior tibia1 nerve stimulation delivered at 2, 5 and 7.5 Hz in 15 healthy subjects. P37 was attenuated significantly at 5 and 7.5 Hz and N50 component attenuated only at 5 Hz, its amplitude remaining stable for further increases of stimulus frequency. Frontal N37 and P50