Biomedical subjects
Publications and source records attributed to M Schieppati.
The Authors give evidence on the function of a pathway mediating somatosensory evoked potentials (SEPs) from muscle nerves, other than the dorsal columns: physiological and anatomical data prove its location to be in the spinothalamic tract. Previous contrasting results on the topic are discussed.
Explore the source record for details and available documents.
The authors describe the technic of elicitation of the H reflex (electrical activity associated with contraction of the triceps muscle of the calf induced by electrical stimulation of the posterior tibial nerve) and the preliminary results of monitoring said reflex in the course of Harrington's operation.
Explore the source record for details and available documents.
Intracellular recordings were performed from bulbar and caudopontine (BcP), rostropontine (rP) and mesencephalic (Mes) neurons in acute encéphale isolé preparations during low- and high-frequency basal forebrain (BF) and hypothalamic (Hyp) stimulation. Low-frequency BF stimulation induced long-latency (7-8 msec) EPSPs on 31% of BcP neurons. High-frequency stimulation of the same regions induced excitation in 58% of them. No inhibition was observed. The descending influences on BcP neurons disappeared after bilateral acute sensorimotor decortication. Low- and high-frequency BF stimulation influenced a very low percentage of rP and Mes neurons. The only effect was a long-latency slow rising EPSP with or without spikes. No inhibition was found in these neurons. Low- and high-frequency Hyp stimulation produced short-latency EPSPs with or without spikes on a large percentage of BcP, rP and Mes neurons. The effect was more constant on rostral (rP) than on caudal (BcP) neurons and more evident when high-frequency stimulation was applied. At high frequency the activation of brain stem neurons paralleled an EEG desynchronization. IPSPs were seen in a low percentage of Mes and rP neurons. Mes neurons could be also activated antidromically. The results suggest that BF regions do not antagonize directly the mesencephalic activating system and may induce electrocortical synchronization through the activation of caudal brain stem neurons. This circuit involves sensorimotor cortical neurons. The facilitatory effect of Hyp stimulation on rostral brain stem neurons indicates that the EEG desynchronization which follows high-frequency Hyp activation may be mediated by the ascending reticular system. Other mechanisms mainly at the diencephalo-telecephalic level may however be involved in this effect.
Explore the source record for details and available documents.
Aim of this study was to assess whether transcutaneous electrical nerve stimulation (TENS) 'gates' somatosensory evoked potentials (EPs) peripherally or centrally, and which afferent fibres and sensory nuclei mediate this effect. The following waves were recorded after stimulation of the median nerve at the wrist or of the digital nerves of the index finger: N9, the cervical N11 and N13, the parietal P9, P11, P14, N18, N20, P22, P27, P40. When both median or digital nerve EPs were conditioned by TENS delivered to the median nerve, reduction in amplitude of N9, P14, N18 and later generated cortical waves was observed. To measure the central contribution to this decrease, unconditioned 'reference' EPs were evoked by stimulating with a current strength yielding an N9 potential of an amplitude equal to that obtained during TENS. In this case, the amplitude of P14, N18 and later cortical waves was significantly greater than during TENS. When both median or digital nerve EPs were conditioned by TENS delivered to the digital nerves, waves were only slightly affected. No effects were seen on the EPs elicited from the median or index finger digital nerves when TENS was administered to the contralateral median or digital nerves or to the ipsilateral middle finger. It is concluded that TENS gates the somatosensory volley, both at a peripheral level through a 'busy line-effect' on large afferent fibres, and centrally at the level of the cuneatus nucleus.
EEGs and short-latency somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded during 151 carotid endarterectomies, performed under general anaesthesia. Carotid occlusion did not affect either EEG or SEP in 120 cases (group A). In 31 cases the EEG showed "ischaemic" abnormalities (group B). A temporary shunt was inserted only in 16 B patients showing also severely depressed cortical SEPs within 2 min after carotid occlusion (group B shunt). In 15 B patients in whom SEPs were less affected, the operation was completed without shunt (group B no shunt). One intraoperative stroke occurred in group A and two in group B shunt. No neurological complications occurred in group B no shunt. Overall stroke rate was 2%. On retrospective analysis, latency and amplitude of N20 and P25 waves proved to be uninfluenced by carotid occlusion in group A, but were significantly affected in group B shunt. P25 amplitude alone was reduced in B no shunt. An arbitrary index (need-for-shunt index, NSI) was made in order to rate changes of P25 latency and amplitude. Its mean values were significantly different in the 3 groups. A threshold value is suggested above which shunt is required, as a useful adjunct to EEG, in order to balance prevention of brain ischaemia against the risks of shunt.
Explore the source record for details and available documents.