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Biomedical subjects

G Cruccu

Publications and source records attributed to G Cruccu.

At least 109 records · Page 6Linked to original sources
PubMed1989

The masseter inhibitory reflex is evoked by innocuous stimuli and mediated by A beta afferent fibres.

Mechanical or electrical stimulations in the area of the mouth evoke two phases of inhibition in the masseter muscle (early and late inhibitory reflex, also called masseter silent periods). The question whether the afferents of the human masseter inhibitory reflex are nociceptive or non-nociceptive has not yet been settled. We showed that an innocuous stimulus, such as a fine jet of saline directed to the lips of healthy humans, evokes an early and a late masseter inhibitory reflex, similar to those following electrical stimulation. We measured the efferent and afferent delay of the masseter early inhibitory reflex in patients submitted to intracranial stimulation of the motor and sensory trigeminal root, and found that the reflex afferents belong to the intermediately-fast conducting fibre group.

Afferent Pathways↗
PubMed1989

Functional organization of the trigeminal motor system in man. A neurophysiological study.

Transcranial stimulation (TCS) in intact human subjects was used to investigate the corticobulbar projections and the functional organization of the trigeminal motor system. Both electrical (with the anode overlying the face area of the motor cortex) and magnetic TCS (with the coil at the vertex) excite the upper motoneurons projecting to the trigeminal motor nucleus, evoking motor potentials (C-MEPs) in the jaw-closing and suprahyoid muscles, but only during voluntary contraction. At least 30% of jaw-closing motoneurons are reached by direct fast-conducting corticobulbar fibres; these projections are mainly crossed. Suprahyoid motoneurons are also reached by fast-conducting corticobulbar fibres; these projections are probably bilateral. In the masseter, electrical TCS also evokes an ipsilateral motor response (R-MEP), followed by a later wave (U), and bilateral inhibitory periods. The R-MEP is secondary to excitation of the motor trigeminal root; the U wave probably results from the simultaneous excitation of Ia afferents in the root and ipsilaterally projecting corticofugal fibres; the inhibitory periods are largely due to activation of exteroceptive afferents in the root. Magnetic TCS, avoiding spread of current to the trigeminal root, evokes C-MEPs but not R-MEPs or U waves. The masseter inhibitory period after magnetic TCS may be due to excitation of corticofugal inhibitory fibres and to mechanical activation of Golgi tendon organs.

Adolescent↗
PubMed1989

Corticospinal potentials after transcranial stimulation in humans.

The descending volley evoked in humans by transcranial electrical stimulation of the scalp was recorded with epidural and spinal electrodes. It consisted of an early wave, which increased in amplitude and decreased in latency when the strength of the stimulus was increased. The mean conduction velocity of the early wave was 66, SD 2.5 m/s. At high stimulus intensity this wave was followed by later and smaller waves, which travel at the same speed as the initial potential. The recovery cycle of the descending volley was studied by delivering paired cortical stimuli at time intervals ranging from 0.5 to 10 ms. The early wave evoked by the test stimulus recovered to about 50% at a 1 ms interval and to 100% at a 3.5 ms interval. The later waves could not be tested at short time intervals but with time intervals longer than 3.5 ms they recovered to 100%. It is suggested that the initial and later waves after scalp stimulation are equivalent to the D and I waves seen in animal experiments.

Adult↗
PubMed1989

Treatment of trigeminal neuralgia by thermocoagulation, glycerolization, and percutaneous compression of the gasserian ganglion and/or retrogasserian rootlets: long-term results and therapeutic protocol.

From 1976 to 1986, 681 patients with drug-refractory trigeminal neuralgia (TN)--typical in 641, symptomatic of multiple sclerosis in 23 and of tumor in 10, atypical in 5, and postherpetic in 2--were treated with various percutaneous procedures. Controlled differential thermocoagulation of the gasserian ganglion and/or retrogasserian rootlets was performed in 533 patients; glycerolization of the trigeminal cistern in 32; and compression of the gasserian ganglion by balloon catheter in 159. Results and complications of each procedure are assessed at a mean follow-up of 6.5 years for thermocoagulation, 5 years for glycerolization, and 3.5 years for compression. The following therapeutic protocol is proposed: 1) in TN patients at first operation: a) gasserian compression (or glycerolization, if experience warrants it) is indicated in all cases of typical TN, unless the 3rd division alone is affected; b) in the latter case and in symptomatic TN, we suggest thermocoagulation; 2) in recurrences: a) after glycerolization or gasserian compression, gasserian compression (or glycerolization) is indicated; b) after thermocoagulation or open surgery, thermocoagulation is suggested.

Catheterization↗
PubMed1988

Correlation between facial involuntary movements and abnormalities of blink and corneal reflexes in Huntington's chorea.

Blink and corneal reflexes were studied in 11 patients with Huntington's chorea and the results compared with the severity of the disease. The latency of the R2 component of the blink reflex was delayed and the duration of R2 and of the corneal reflex (CR) prolonged. A greater habituation of the R2 component was found in the patients with involuntary movements in the face, and in some patients a long-lasting depression of R2 was present. A correlation was found between: (a) severity of involuntary face movements and R2 and CR latency and (b) severity of involuntary movements in the neck and latency of R2.

Adolescent↗
PubMed1988

Stimulation of motor tracts in multiple sclerosis.

Percutaneous electrical stimulation of the motor cortex was used to evaluate corticospinal conduction to upper-limb motoneurons in 29 patients with multiple sclerosis. Central motor conduction abnormalities were correlated with clinical signs and somatosensory evoked potentials. Muscle responses to cortical stimulation were altered in 20 patients. The most common abnormality was increased central motor conduction time; in two cases the responses to cortical stimulation were absent. Abnormalities were also present in patients with no clinical evidence of corticomotoneuron deficit. Alterations of muscle responses and of somatosensory evoked potentials were usually correlated, but may appear independently. Both testing methods are useful in the study of patients with multiple sclerosis.

Adult↗
PubMed1988

Impairment of masticatory function in hemiplegia.

We studied masseter muscle function in 15 hemiplegic patients. Direct motor responses to stimulation of the masseteric nerve were normal. Voluntary activity at maximum strength was reduced on the paretic side. The jaw jerk was symmetric, but facilitation by teeth clenching showed on the nonparetic side only. Masseter silent periods were ill-defined and prolonged in recordings from the paretic side. The second silent period, but not the first, was reduced in size when the paretic side was stimulated, and showed an increased habituation. Though the masticatory nucleus receives bilateral innervation, the contralateral hemisphere exerts a predominant control on voluntary activity and multisynaptic reflexes.

Adult↗
PubMed1987

Corneal and blink reflexes in Parkinson's disease with "on-off" fluctuations.

In 13 patients with Parkinson's disease and "on-off" fluctuations and in a control group, the electrically evoked blink (R1 and R2 component) and corneal reflexes (CR), the habituation of the glabellar reflex, and the blink rate were studied. Latency, amplitude, and recovery cycle of R1 was normal. CR latency, but not R2 latency, was significantly shorter in patients than in normal subjects. R2 recovery cycle, but not CR recovery cycle, was facilitated in "off" patients in comparison to normal subjects. CR and R2 duration was longer in "off" than in "on" patients. R2 recovery cycle became similar to that of normal subjects after fluctuation from "off" to "on" period, but CR recovery cycle varied only slightly. The habituation of the glabellar reflex and the blink rate were decreased in "off" patients. These findings indicate that the enhanced excitability of R2 is related to the central dopamine activity levels. The differences between the recovery cycles of CR and R2 may be explained with the smaller number of interneurons subserving CR than R2 circuit. The shorter latency of CR, but not of R2, both in "on" and "off" patients, may suggest that in Parkinson's disease basal ganglia exert a different control of incoming sensory input transmitted via beta and delta fibers.

Adult↗
PubMed1987

The 'foramen ovale electrode': a safe tool to study temporal lobe epilepsy.

Following the description by Wieser et al. (1985) of the use of a foramen ovale electrode to record from mesial temporal structures the authors describe an alternative electrode equipped with radial tines to make it self-retaining. A helical section provides flexibility along the electrode's longitudinal axis preventing displacement of the tip during jaw movements. Clinical and detailed neurophysiological examinations failed to demonstrate any evidence of motor or sensory trigeminal nerve dysfunction and no complications were encountered.

Electrodes, Implanted↗
PubMed1987

Intracranial stimulation of the trigeminal nerve in man. III. Sensory potentials.

Percutaneous electrical stimulation of the trigeminal root was performed in 18 subjects undergoing surgery for idiopathic trigeminal neuralgia or implantation of electrodes into Meckel's cave for recording of limbic epileptic activity. All subjects had normal trigeminal reflexes and evoked potentials. Sensory action potentials were recorded antidromically from the supraorbital (V1), infraorbital (V2) and mental (V3) nerves. In the awake subject, sensory potentials were usually followed by myogenic artifacts due to direct activation of masticatory muscles or reflex activation of facial muscles. In the anaesthetised and curarised subject, sensory potentials from the three nerves showed 1.4-2.2 ms onset latency, 1.9-2.7 ms peak latency and 17-29 microV amplitude. Sensory conduction velocity was computed at the onset latency (maximum CV) and at the peak latency (peak CV). On average, maximum and peak CV were 52 and 39 m/s for V1, 54 and 42 m/s for V2 and 54 and 44 m/s for V3. There was no apparent difference in CV between subjects with trigeminal neuralgia and those with epilepsy. A significant inverse correlation was found between CV and age, the overall maximum CV declining from 59 m/s (16 years) to 49 m/s (73 years). This range of CV is compatible both with histometric data and previous electrophysiological findings on trigeminal nerve conduction. Intraoperative intracranial stimulation is also proposed as a method of monitoring trigeminal function under general anaesthesia.

Action Potentials↗
PubMed1987

Neurophysiologic assessment of trigeminal function after surgery for trigeminal neuralgia.

To assess the function of the three trigeminal divisions, we studied corneal reflex, early and late blink reflexes, early and late masseter silent periods, and jaw jerk in normal subjects and in 35 patients submitted to surgery for trigeminal neuralgia. The corneal reflex was most sensitive to thermocoagulation and the jaw jerk to microcompression; the other reflexes showed an intermediate behavior, depending on afferent fiber size. Trigeminal function was less impaired after microcompression and recovered earlier than after thermocoagulation.

Adult↗
PubMed1986

Inhibition of jaw-closing muscles by electrical stimulation of the ophthalmic division in man.

High-intensity stimulation of the supraorbital region elicits, together with a blink reflex, a reflex inhibition of the jaw-closing muscles in normal man. The response differs from the well known inhibition obtained by intra- and perioral stimulation in two main features. Firstly, it consists of a single late silent period (SP), only occasionally preceded by a short and partial decrease of the background EMG activity; secondly, the inhibitory response appears at a rather high threshold, requiring a stimulus intensity which is 4-fold the sensory perception threshold and 3-fold that required to evoke the blink reflex. Electrical and mechanical stimulation of the cornea failed to evoke a significant inhibitory reflex. The silent period and the blink reflex were similarly affected by local anaesthetic infiltration of the supraorbital skin, suggesting that the afferents subserving the two reflexes belong to the same fibre group; the higher threshold of the supraorbital inhibitory response may be explained by the need for a larger spatial summation. The considerable latency gain and relatively rapid habituation shown by the supraorbital inhibitory response imply a multisynaptic circuit, similar to that responsible for the second silent period which occurs following 'oral' stimulation. A common interneuronal net for these two reflexes is suggested by the results of interaction experiments employing combined supra- and infraorbital stimulation.

Adult↗
PubMed1986

Excitability of the corneal reflex in man.

The corneal reflex evoked by electrical stimulation of the corneal mucosa and the blink reflex evoked by electrical stimulation of the supraorbital nerve were recorded in 8 normal subjects. Habituation to repetitive stimulation and the recovery cycle to double shock were studied. The corneal reflex habituated significantly to repetitive stimulations at a rate of 0.2-1 Hz but was more resistant than the late component of the blink reflex (R2). There was a clear dissociation between the recovery of the corneal reflex and that of R2; the corneal reflex was again less affected by the proceeding impulse. These results suggest that the corneal reflex is relayed through fewer intramedullary synapses than R2.

Adult↗
PubMed1986

Intracranial stimulation of the trigeminal nerve in man. I. Direct motor responses.

Direct electrical stimulation of the intracranial portion of the trigeminal nerve was performed in 23 subjects undergoing retrogasserian thermocoagulation for the treatment of idiopathic trigeminal neuralgia. In 16 subjects, who were having the operation for the first time, neurological examination was normal, as was neurophysiological testing of trigeminal function. Seven subjects were being operated for the second time, owing to a recurrence of symptoms. In all the subjects being operated for the first time, direct motor responses were obtained from ipsilateral temporalis, masseter and anterior belly of the digastric. The motor conduction velocity was equal for the fibres directed to all three muscles. This was estimated to be 54m/s in the masseteric nerve and 55-68 m/s in the intracranial portion of the trigeminal nerve. Patients who had undergone previous thermocoagulation had a considerably slower conduction velocity. It is supposed that myelin sheaths had been damaged at the first operation.

Electric Stimulation↗
PubMed1986

Intracranial stimulation of the trigeminal nerve in man. II. Reflex responses.

The reflex responses evoked by direct electrical stimulation of the intracranial portion of the trigeminal nerve have been studied in 16 subjects undergoing percutaneous retrogasserian thermocoagulation for the treatment of trigeminal neuralgia affecting the second or third division. In the obicularis oculi muscle, early and late responses similar to the R1 and R2 components of the blink reflex were recorded. The former could be evoked only by stimulation of the second division and its latency was consistent with intermediately fast afferents. A late reflex (50-70 ms) was occasionally recorded from the anterior belly of the digastric muscle. The response was sometimes followed by a later activity and showed the features of a polysynaptic reflex. No response was obtained in the jaw elevators when fully relaxed. With the subject voluntarily clenching his teeth, both an early "H-like" response and two silent periods in the background EMG were obtained. The second silent period was similar in the muscles ipsi- and contralateral to intracranial stimulation, while the first silent period was longer in the ipsilateral muscles. Possible mechanisms contributing to the inhibition following stimulation of the mixed portion of the nerve are discussed.

Electric Stimulation↗