EMG responses in the soleus muscles evoked by unipolar galvanic vestibular stimulation

This study compared the effects of transmastoid galvanic stimulation with unilateral galvanic stimulation of vestibular afferents. We recorded the effects on soleus EMG occurring at short (SL) and medium (ML) latency, both in normal subjects and in patients with previous unilateral vestibular neurectomy. Unipolar cathodal and anodal stimulation on the same side produced opposite effects for both SL and ML responses. Responses to unilateral cathodal or anodal stimulation were smaller, but otherwise resembled those of transmastoid stimulation with the cathode or the anode placed on the same side, respectively. Unilateral cathodal stimulation resulted in a larger SL response, which occurred at shorter latency than unilateral anodal stimulation. With unipolar stimulation on the side of previous vestibular nerve section, typical SL and ML responses were absent. With stimulation of the intact side, the patients showed smaller SL responses than normal subjects with unilateral stimulation. The larger responses to unilateral cathodal compared to unilateral anodal stimulation are consistent with previous reports that cathodal stimulation produces an increase and anodal a decrease in vestibular nerve firing. The smaller SL responses in the patients may be a consequence of central nervous system reorganization following unilateral vestibular nerve section.

Endogenous histamine stimulates ischemically sensitive abdominal visceral afferents through H1 receptors

Abdominal ischemia stimulates sympathetic visceral afferents to reflexly activate the cardiovascular system. We have shown previously that topical application of histamine (HA) to the gastric wall causes reflex cardiovascular responses and have documented increased histamine concentrations in intestinal lymph and portal venous plasma during brief abdominal ischemia. In the present study, we hypothesized that histamine produced during ischemia activates ischemically sensitive C-fiber afferents by stimulation of H1 receptors. Nerve activity of single-unit abdominal visceral C-fiber afferents was recorded from the right thoracic sympathetic chain of anesthetized cats. Injection of histamine (25 micrograms/kg ia) significantly increased activity of nine ischemically sensitive C fibers from 0.09 +/- 0.06 to 1.11 +/- 0.20 imp/s. An H1-receptor agonist, 2-(3-chlorophenyl)histamine (250 micrograms/kg ia), also increased activity of these afferents from 0.11 +/- 0.04 to 0.64 +/- 0.18 imp/s (P < 0.05). Furthermore, an H1-receptor antagonist (pyrilamine, 0.2 mg/kg i.v.) significantly attenuated the increased activity in 11 other C fibers from 0.91 +/- 0.16 to 0.35 +/- 0.06 imp/s ischemia vs. pyrilamine + ischemia) and eliminated the response of 9 separate ischemically sensitive afferents to histamine. Conversely, both the H2-receptor agonist dimaprit (500 micrograms/kg ia) and the H3-receptor.agonist (R)-alpha-methylhistamine (250 micrograms/kg ia) did not significantly alter the activity of these nine afferents. In nine separate cats treated with indomethacin (5 mg/kg i.v.), pyrilamine (0.2 mg/kg i.v.) further significantly attenuated the increased activity in seven of nine C fibers during ischemia, and indomethacin (5 mg/kg i.v.) attenuated the response of eight other afferents to histamine. These data suggest that during mesenteric ischemia endogenous histamine contributes to the activation of afferents through direct stimulation of histamine H1 receptors and that histamine's stimulating effect on these afferents is dependent partially on production of prostaglandins.

Central gain of the cardiac sympathetic afferent reflex in dogs with heart failure

Previous studies from our laboratory have shown that the cardiac sympathetic afferent reflex is enhanced in dogs with experimental heart failure. The aim of the present study was to determine if the central gain of the cardiac sympathetic afferent reflex was also enhanced in dogs with heart failure. Fifteen dogs with pacing-induced heart failure were used in this study. Seventeen sham-operated dogs served as control. At the time of the acute experiment the dogs were anesthetized with alpha-chloralose. Arterial blood pressure, heart rate, and renal sympathetic nerve activity were recorded. After sinoaortic denervation and cervical vagotomy, a thoracotomy was performed in the second intercostal space. The left stellate ganglion was identified, and the left cardiac sympathetic nerves were cut. The central end of the left cardiac sympathetic nerves was placed on bipolar stimulating electrodes. The renal sympathetic nerve activity responses to electrical stimulation (30 Hz, 1 ms with varying voltages from 1 to 10 V; or 10 V, 1 ms with varying frequencies from 1 to 30 Hz) of the afferent cardiac sympathetic nerves were compared between sham and heart failure groups. Reflex renal sympathetic nerve activity responses to stimulation of the cardiac sympathetic nerves were significantly greater in the heart failure group compared with that in the sham group (21.4 +/- 3.2 vs. 9.8 +/- 2.9% at 10 V, 30 Hz and 27.7 +/- 4.5 vs. 9.9 +/- 3.4% at 30 Hz, 10 V, heart failure vs. sham group, respectively; for both relationships, P < 0.05). This enhanced central gain of the cardiac sympathetic afferent reflex in the heart failure group was significantly attenuated after intravenous and cerebroventricular injection of the angiotensin II receptor antagonist losartan (5 mg/kg i.v. and 0.125 mg/kg in 0.1 ml i.c.v.). These data suggest that the central gain of the cardiac sympathetic afferent reflex is enhanced in dogs with heart failure and central angiotensin II plays an important role in this enhanced response.

Idiopathic focal dystonia: a disorder of muscle spindle afferent processing?

As muscle spindles are involved in the sensation of position and movement of the body, we tested their involvement in the pathophysiology of idiopathic focal dystonia. Twenty patients with torticollis, nine with writer's cramp, two with blepharospasm and 16 healthy control subjects participated. In the first task, the blindfolded subject matched the position of the passively moved forearm with the opposite forearm when the elbow joint was slowly flexed. In a second matching task, passive movement was replaced by stimulation of one biceps tendon with a 50-Hz vibratory stimulus (a selective stimulus for muscle spindle Ia afferents). In normal individuals, this stimulus produces flexion of the vibrated arm around the elbow joint. Movement in both arms was recorded electronically. In experiments without vibratory stimuli, dystonic subjects showed normal movement of the tracking arm during attempts to match the position of the passively moved arm and no difference between the arms in the initial and final steady state positions. In experiments using vibratory stimuli, vibration of biceps tendons in normal subjects elicited flexion of the stimulated arm at the elbow and a matching movement of the opposite arm. In patients with dystonia, there was a similar flexion response to the vibratory stimulus in the stimulated arm but movement of the tracking arm was reduced. Taken together, these experiments suggest that there is abnormal perception of motion, but not position, in dystonic subjects. Dystonic subjects showed bilateral abnormalities of perception of the tonic vibration reflex which were remote from the clinically affected site. These findings are discussed in relationship to the role of muscle spindle Ia afferents in focal dystonia.

The mechanism of action of botulinum toxin type A in focal dystonia is most probably through its dual effect on efferent (motor) and afferent pathways at the injected site

OBJECTIVE

To highlight some clinical and physiological features related to treatment with botulinum toxin type A (BTX-A) injections for focal dystonia that may suggest an effect through efferent (alpha motoneuron) and afferent pathways.

DATA SOURCES

This review is based on published clinical and physiological studies as well as personal experience regarding the effect of BTX-A in focal dystonia.

DATA SYNTHESIS

Long or short lag period between BTX-A injections and clinical improvement, remote effect, an effect on the basic physiological characteristics of dystonia, poor correlation between the local weakness and the clinical improvement and alleviation of pain are clinical observations which are difficult to explain on the basis of the known effect of BTX-A on the neuromuscular junction of the alpha motoneuron. These observations as well as recent scientific reports are used to discuss a hypothesis that in addition to its effect as local muscle relaxant, BTX-A acts at the level of the central nervous system (CNS) for 'reorganization'. Such an effect on CNS activity can be mediated through afferent pathways coming from the injected site--possibly originated in muscle spindles. Its effect through afferent pathways on the CNS may be considered as a long-term 'sensory trick'.

Attenuated response of renal mechanoreceptors to volume expansion in chronically hypoxic rats

Multifiber renal afferent nerve activity responds to volume expansion in sea level rats but not in chronically hypoxic (high altitude) rats. We performed single-unit recordings of renal afferent nerve activity to characterize renal sensory receptors and their responses to volume expansion in these animals. Hypoxia was induced by placing Wistar rats in an altitude chamber (380 Torr, 5,500 m) for 4 wk. Spontaneously firing renal R2 chemoreceptor and arterial, ureteropelvic, and venous mechanoreceptors were identified. The basal activity of each receptor was similar among these rats. In response to specific stimulus, the increasing impulse of R2 chemoreceptor was similar between two groups of rats, but the increasing activity of each mechanoreceptor was less in hypoxic rats. When challenged with saline load, R2 chemoreceptor activity decreased, but all mechanoreceptors activated in all rats. Despite similar increases of arterial, renal ureteropelvic, and venous pressure during saline load, the increasing activity of each mechanoreceptor was significantly less in hypoxic rats. These results indicated chronic hypoxia attenuates the sensitivity of renal mechanoreceptors in response to the stimulation of saline load.

Median nerve middle-long latency somatosensory evoked potentials in children with tactile evoked spikes

It is known that hand tapping during electroencephalography (EEG) recording evokes centrotemporal spikes in some 4- to 12-year-old children. This phenomenon occurs in both healthy and epileptic children. The same children were reported to show giant middle-long latency evoked potentials (MLSEPs). To study the relationship between tactile evoked spikes (TES) and MLSEPs, we performed a neurophysiologic investigation in 25 children with TES and in 25 children without any EEG abnormality. Such an investigation included a MLSEP study after both electrical and tactile stimulation with simultaneous recording of digital EEG. MLSEPs consistently showed three negative (NI, NII, NIII) and two positive (PI, PII) peaks. Children with TES had MLSEPs of enlarged amplitude. The analysis of MLSEPs and TES characteristics led us to the conclusion that they are the same neurophysiologic event, with NII being the evoked spike and NIII the following slow-wave.

Plasma protein extravasation induced in the rat dura mater by stimulation of the parasympathetic sphenopalatine ganglion

It has been proposed that migraine could result from a neurogenic inflammation of the dura mater. According to this theory, inflammation could be initiated by an axon reflex of nociceptive nerve fibers, but the trigger of this axon reflex remains poorly understood. Previous works have shown that parasympathetic agonists can activate mast cells and/or sensory C-fibers, inducing pain and inflammation. The aim of the present work was to determine whether the activation of intracranial parasympathetic nerve fibers could trigger an inflammatory mechanism within the rat dura mater. Activation of the intracranial parasympathetic system was achieved by electrical stimulation of the sphenopalatine ganglion (SPG). The development of a neurogenic inflammation was estimated either by microscopic examination or by quantitative measurement of plasma protein extravasation (PPE) in the dura. To determine the respective roles of the parasympathetic and sensory innervations, two groups of rats were pretreated either with atropine or with capsaicin. Stimulation of the SPG induced a PPE increase of about 200% in the stimulated side on the dura mater. Extravasated material was mainly concentrated around small blood vessels. This extravasation was significantly reduced by capsaicin pretreatment and completely abolished by atropine. Infusion of carbachol in the common carotid artery induced PPE in the ipsilateral dura comparable to that induced by electrical stimulation of the SPG. This extravasation was also blocked by atropine infusion. These data indicate for the first time that the parasympathetic nervous system can trigger a neurogenic inflammation in the dura via muscarinic cholinergic receptors. Sensory C-fibers seem to play a role in this phenomenon. With respect to the potential autonomic imbalance described in the etiology of various types of vascular headaches, such a mechanism could be important in inducing attacks.

The late blink reflex response abnormality due to lesion of the lateral tegmental field

We report on a blink reflex abnormality observed in two patients, which provides additional information on the central pathways mediating this reflex. Autopsy was performed in one patient and MRI in the other. In the first patient there was a small lesion at the dorsal middle third of the lateral tegmental field and in the second patient at the level of the dorsal lower third of the medulla oblongata. In both patients the common finding was the absence of the late response (R2) ipsilateral to the side of the lesion, while the R2 response on the unaffected side was normal regardless of the side of the supraorbital nerve stimulation. The R1 responses were normal. This type of blink reflex abnormality has not been reported before and is referred to by us as 'tegmental type' of R2 abnormality. The results led to the conclusions that: (i) the crossed and uncrossed ascending trigeminofacial connections are mediated through the lateral tegmental field; (ii) the uncrossed trigeminofacial connection originates at the level of at least the lower medulla oblongata; (iii) the contralateral R2 response is established by way of an ascending pathway, which crosses the midline at the level of at least the lower third of the medulla oblongata.

Recent concepts in the pathophysiology and evaluation of spasticity

Spasticity is still a challenge to clinicians and scientists. The participation of Ia, Ib, II, III and IV afferents pathways, as well as those related with presynaptic inhibition. Renshaw cells modulation, and alpha and gamma motoneurons hyperexcitability, in this medical problem are reviewed. A brief overview on the more common neurophysiological tests performed during the evaluation of human spasticity is presented.

[The analgesic and antidepressant action of adrenaline-induced stress in the endogenous activation of the gastric afferent systems in rats]

Adrenaline-induced stress as well as exogenous cholecystokinin exerted analgetic, antidepressant, and antistress effect upon depressive rats with high nociceptive sensitivity. The effect seems to be due to stimulation of chemoreceptors of the stomach vagal afferents by means of cholecystokinin secretion into the gastric lumen.

Functional MR activation correlated with intraoperative cortical mapping

PURPOSE

To evaluate the spatial specificity of functional MR imaging by comparing it with intraoperative electrocortical mapping.

METHODS

Functional MR imaging was performed in 28 patients before awake craniotomy and intraoperative electrocortical mapping. Activation was mapped for finger movement, lip movement, tongue movement, word generation, and counting paradigms. During surgery, finger movement, lip movement, tongue movement, counting, and/or speaking were mapped. The functional images and the photographic recordings of the brain functions mapped during surgery were converted to bit maps and coregistered by a computer program. The distance between the intraoperatively mapped function site and the MR activation site for a comparable function was measured.

RESULTS

Forty-six functions were recorded on MR images and intraoperative maps. In 100% of correlations, the intraoperative site and the MR activation site were within 20 mm; in 87% of correlations they were within 10 mm. For each paradigm, 67% or more of the intraoperative stimulation maps correlated within 10 mm of the MR activation site.

CONCLUSIONS

For the tasks used in this study, the activation site on functional MR images correlated well with the site at which intraoperative stimulation identified function.

Reflex influences on renal nerve activity characteristics in nephrosis and heart failure

Cardiac baroreflex regulation of efferent renal sympathetic nerve activity (ERSNA) is abnormal in nephrotic syndrome (NS). The purpose of the present study was to examine the responses of amplitude and frequency of synchronized ERSNA discharge in anesthetized NS rats subjected to reflex maneuvers that alter the activity of and the interaction between aortic and cardiac baroreceptors. Steady-state ERSNA was analyzed in three groups of anesthetized rats: control, NS, and congestive heart failure (CHF) (in the latter, the defect in cardiac baroreflex regulation of ERSNA is peripheral rather than central). In protocol A, analysis was performed during control, after bilateral aortic depressor nerve section, after bilateral cervical vagus nerve section, and during central vagus nerve stimulation (VAGSTIM). In protocol B, analysis was performed during control, after bilateral cervical vagus nerve section, after bilateral aortic depressor nerve section, and during central aortic depressor nerve stimulation. In protocol A, VAGSTIM decreased ERSNA and peak height (fewer active fibers), but not peak frequency, in control and CHF but not NS rats. In NS rats, this lack of effect of VAGSTIM was specific for ERSNA, because depressor and bradycardia responses to VAGSTIM were unaffected. In protocol B, central aortic depressor nerve stimulation decreased ERSNA and peak height, but not peak frequency, in control, CHF, and NS rats similarly. It is concluded that the defect in cardiac baroreflex function in NS is specific for ERSNA, is central rather than peripheral, and affects the number of active renal sympathetic nerve fibers rather than their firing frequency.

Pain-related and electrically stimulated somatosensory evoked potentials in patients with Machado-Joseph disease and multiple system atrophy

We investigated the ascending somatosensory pathway for pain in 8 patients with Machado-Joseph disease (MJD) and multiple system atrophy (MSA). Pain-related somatosensory evoked potentials (pain SEPs) by CO2 laser stimulation were examined together with conventional electrically stimulated somatosensory evoked potentials (electric SEPs). The sporadic cerebellar ataxia of patients with MSA showed a normal pattern of pain SEPs as well as electric SEPs. However, pain and electric SEPs were abnormal for the central and/or peripheral ascending pathway in MJD. These abnormalities of pain and electric SEPs in MJD were not related to the clinical severity of sensory impairment, but they indicate that MJD presents a subclinical abnormality for the ascending somatosensory pathways not only for vibratory sense but also for pain sense.

Selective ablation of rat knee joint innervation with injected immunotoxin: a potential new model for the study of neuropathic arthritis

Neuropathic arthropathy is a severe chronic degenerative condition associated with decreased or absent sensory innervation of the involved joint. Existing animal models of neuropathic arthritis are limited by the technical difficulties of obtaining either highly selective or complete joint denervation in a minimally invasive fashion. We undertook experiments to determine the feasibility of using the newly described method of selective neuronal lesioning with injected immunotoxin as a means of creating a more tractable model of neuropathic arthritis. Retrograde tracing with fluorochrome revealed that the knee joint of the female Wistar rat is supplied by 581 +/- 31 (mean +/- SD) joint afferents. Immunohistochemistry confirmed that virtually all sensory neurons in the rat express the cell surface receptor Thy 1. Injection of rat knee joints with an immunotoxin targeted toward Thy 1 resulted in the selective ablation of an average of 88% of the joint afferents identified with fluorochrome that are normally found in the ipsilateral L3 and L4 ganglia.

Effects of lesions invading the postcentral gyrus on somatosensory thresholds on the face

Patients with unilateral removals from either the parietal, frontal or temporal lobe and normal control subjects were examined on three tests of tactile sensibility. The patients with surgical excisions from the parietal lobe were subdivided into two groups: those whose lesions invaded the face area in the primary sensory cortex and those whose lesions spared this area. A significant percentage of patients with lesions that invaded the face area had mild to severe sensory deficits on the side of the face contralateral to the lesion. A much smaller number of patients had deficits on the ipsilateral side. Lesions to the face area in the primary sensory cortex were, however, associated with a lower incidence of severe and persistent sensory deficits when compared to previous results on the effects of lesions to the hand area on the sensory capacity of the hand. These results suggest that there is some preservation of sensory function after damage to the face area in the primary sensory cortex, presumably due to the bilateral representation of the face.

The evaluation of mannitol therapy in acute ischemic stroke patients by serial somatosensory evoked potentials

The effects of mannitol infusion therapy on acute ischemic stroke were investigated by serial median nerve somatosensory evoked potentials (SEP) in 31 patients with abnormal SEP recordings within 72 hours after onset. In 10 patients with missing N20 waves mannitol had no effect. In 12 patients mannitol improved N20 and central conduction time (CCT) latencies. In 9 patients absent N20 waves appeared after mannitol. As regard to the location of infarcts, CT revealed 7 hemispheric infarcts in patients with absent N20 waves in spite of mannitol infusion. The remaining patients' CTs revealed cortical and subcortical infarcts. This study concludes that mannitol treatment improved microcirculatory flow in the ischemic penumbra of acute ischemic stroke patients. We suggest that SEPs can be used in evaluating the effects of drugs to be used in the therapy of acute cerebrovascular accidents.

Sigmoid afferent mechanisms in patients with irritable bowel syndrome

Up to 60% of patients with IBS have lowered perception thresholds in the rectum to balloon distension. The current study sought to test the hypothesis that IBS patients with normal perception thresholds in the rectum show hypersensitivity of afferent pathways in the sigmoid colon. Eleven healthy normal subjects and eight IBS patients with normal rectal perception thresholds underwent a balloon distension protocol in the sigmoid and rectum. Discomfort thresholds, receptive relaxation, compliance, and referral patterns were measured. Although IBS patients had significantly lower discomfort thresholds in the sigmoid when measured as volume, pressure, and wall tension, thresholds were similar to normals. Receptive relaxation and dynamic compliance were significantly decreased in IBS patients in the sigmoid. Referral patterns were similar during sigmoid distention in IBS patients in comparison to normals. Despite normal perception thresholds in rectum and sigmoid, IBS patients show evidence for alterations in rectosigmoid afferent mechanisms. In the sigmoid, this is seen in the form of reduced reflex relaxation and compliance and in the rectum in the form of altered viscerosomatic referral.

Functional MRI of pain- and attention-related activations in the human cingulate cortex

The aims of the study were to use functional magnetic resonance imaging (fMRI) to 1) locate pain-related regions in the anterior cingulate cortex (ACC) of normal human subjects and 2) determine whether each subject's pain-related activation is congruent with ACC regions involved in attention-demanding cognitive processes. Ten normal subjects underwent fMRI with a 1.5-T standard commercial MRI scanner. A conventional gradient echo technique was used to obtain data from a single 4-mm sagittal slice of the left ACC, approximately 3.5 mm from midline. For each subject, interleaved sets of 6 images were obtained during a pain task, an attention-demanding task, and at rest, for a total of 36 images per task. Pain of different intensities was evoked via electrical stimulation of the right median nerve. The attention-demanding task consisted of silent word generation (verbal fluency). Additional experiments obtained data from the right ACC. A pixel-by-pixel statistical analysis of task versus rest images was used to determine task-related activated regions. The pain task resulted in a 1.6-4.0% increase in mean signal intensity within a small region of the ACC. The exact location of this activation varied from subject to subject, but was typically in the posterior part of area 24. The signal intensity changes within this region correlated with pain intensity reported by the subject. The attention-demanding tasks increased the mean signal intensity by 1.3-3.3% in a region anterior and/or superior to the pain-related activation in each subject. The activated region was typically larger than the pain-related activation. In some cases this activation was at or superior to the ACC border, near the supplementary motor area. These regions did not show any pain-intensity-related activation. In one subject both right and left ACC were imaged, revealing bilateral ACC activation during the attention task but only contralateral pain-related activation. These findings shed light on pain- and attention-related cognitive processes. The results provide evidence for a region in the posterior part of the ACC that is involved in pain and a more anterior region involved in other attention-demanding cognitive tasks.

Mechanisms and implications of autonomic nervous system dysfunction in heart failure

Neurohumoral activation characterizes heart failure. Patients with the greatest amount of neurohumoral activation, as estimated by plasma norepinephrine levels, have the worst prognosis. The fundamental mechanisms underlying this neurohumoral activation remain unknown, however. Recent data support the hypothesis that early sympathetic dysregulation in heart failure is attributable to early attenuation of cardiac and arterial baroreceptor control of sympathetic nerve activity. Neurohumoral excitation is organ specific, affecting the heart first. Neurohumoral activation follows a stepwise pattern, with resistance to atrial natriuretic peptide and marked sympathetic activation characterizing a transition period from left ventricular dysfunction to overt heart failure. Renin-angiotensin-aldosterone system activation then occurs. Additional abnormalities of afferent systems, such as augmented muscle metaboreceptor sensitivity and increased peripheral chemoreceptor sensitivity, may modulate the sympathetic activation in established heart failure. Brain ouabainlike activity has been shown to cause sympathetic excitation in two animal models of heart failure and may play a key (although presently undefined) role in neurohumoral excitation in humans with heart failure. Therapies that interrupt, or even reverse, the neurohumoral activation in heart failure hold the greatest promise for the growing patient population afflicted with this syndrome.

Spatiotemporal aspects of sympathetic C-fiber afferent activity in pressor reflex during abdominal ischemia

Activation of abdominal sympathetic visceral afferents during ischemia elicits excitatory cardiovascular reflexes. The present study examined the time course and discharge patterns of activation of ischemically sensitive sympathetic C-fiber afferents, and then the relationship between summated afferent activity and the pressor reflex induced by prolonged abdominal ischemia was determined. Single-unit activity of abdominal C-fiber afferents was recorded from the right thoracic sympathetic chain of anesthetized cats during 30 min of ischemia. The reflex pressor response to abdominal ischemia was induced by occlusion of celiac and superior mesenteric arteries. Of 68 C-fiber afferents studied, 36 (approximately 53%) were activated during 30 min of ischemia, whereas the activity of the remaining 32 were not altered. Onset latencies of 36 C-fiber afferents activated by ischemia ranged from 1.0 to 17.4 min with an average of 6.1 +/- 0.8 min. The majority of activated afferents manifested a bursting pattern of discharge activity as ischemia was prolonged beyond 10 min. Summated response of activated afferents, but not individual afferent activity, was related closely to the reflex pressor response during 30 min of ischemia. These results suggest that both recruitment of sufficient numbers of C-fiber afferents and adequate discharge frequency of afferents constitute an encoding mechanism for the pressor reflex during abdominal ischemia.

Magnetic stimulation of the descending and ascending tracts at the foramen magnum level

To test the possibility that stimulation over the foramen magnum activates ascending tracts as well as descending tracts, we studied 4 patients with myoclonic epilepsy all of whom had enhanced cortical long loop reflexes (LLRs) and 10 normal subjects, using our previously reported method (Ugawa et al., Ann. Neurol., 1994, 36: 618-624). For latency comparisons, peripheral nerve stimulation at the elbow and spinal motor root were also performed. In all patients, magnetic stimulation at the foramen magnum consistently elicited long loop reflexes as well as direct responses caused by stimulation of the descending tracts. In contrast, no LLRs were ever seen in any normal subjects. The latencies of both types of response were the same whether stimulation used upward or downward current in the brain, although the former was always more effective. This indicates that stimulation at the level of the foramen magnum activates ascending tracts as well as descending tracts at a fixed position. The threshold for LLRs was lower than that for activation of the descending tracts. This threshold difference is compatible with the hypothesis that large diameter fibers from muscle afferent conduct the central afferent volley for LLRs (Marsden et al., Brain, 1977, 100: 185-200).