Hind leg ataxia of cervical origin and cervico-lumbar spinal interactions with a supratentorial pathway

Association of Head Injury, Neck Injury or Acoustic Trauma on Phenotype of Ménière's Disease

The aim of the present study was to investigate adverse effects of head injury, neck trauma, and chronic noise exposure on the complaint profile in people with Ménière's disease (MD). The study used a retrospective design. Register data of 912 patients with MD from the Finnish Ménière Federation database were studied. The data comprised case histories of traumatic brain injury (TBI), neck trauma and occupational noise exposure, MD specific complaints, impact related questions, and the E-Qol health-related quality of life instrument. TBI was classified based on mild, moderate, and severe categories of transient loss of consciousness (TLoC). The mean age of the participants was 60.2 years, the mean duration of the disease was 12.6 years, and 78.7% were females. Logistic regression analysis, linear correlation, and pairwise comparisons were used in evaluating the associations. 19.2% of the participants with MD had a history of TBI. The phenotype of participants with TBI was associated with frequent vestibular drop attacks (VDA), presyncope, headache-associated vertigo, and a reduction in the E-QoL. Logistic regression analysis explained the variability of mild TBI in 6.8%. A history of neck trauma was present in 10.8% of the participants. Neck trauma associated with vertigo (NTwV) was seen in 47 and not associated with vertigo in 52 participants. The phenotype of NTwV was associated with balance problems, VDA, physical strain-induced vertigo, and hyperacusia. Logistic regression analysis explained 8.7% of the variability of the complaint profile. Occupational noise exposure was recorded in 25.4% of the participants and correlated with the greater impact of tinnitus, hyperacusis, and hearing loss. Neither the frequency, duration, or severity of vertigo or nausea were significantly different between the baseline group and the TBI, NTwV, or noise-exposure groups. The results indicate that TBI and NTwV are common among MD patients and may cause a confounder effect.

Reflex transmission to lumbar α-motoneurones in the mouse similar and different to those in the cat

Investigation and interpretation of defective motor circuitries in transgenic mice required further basic results from wild-type mice. Therefore, we investigated the lumbar motor reflex pattern in anaesthetised mice using intracellular motoneuronal recording and monosynaptic reflex testing. Thresholds and latencies in mice were similar to those in cats: thresholds for monosynaptic (group I) EPSPs were slightly above 1T (T=threshold for the lowest threshold fibres), around 1.5T for group II EPSPs and above 10T for group III EPSPs; group I EPSPs were maximal with a stimulus strength around 2T, group II EPSPs were maximal with 5-8T; latencies to the group I incoming volley were below 1ms for monosynaptic group I EPSPs, around 3ms for polysynaptic group II EPSPs and above 4ms for polysynaptic group III EPSPs. In contrast to reflex actions in the cat, monosynaptic gastrocnemius-soleus reflexes were facilitated by conditioning stimulation of the peroneal, sural and tibial nerves, i.e. by a variety of different, probably flexor reflex afferents. This facilitation persisted after high lumbar spinalisation indicating an independency to supraspinal influences. Nociceptive muscle afferents facilitated the peroneal monosynaptic reflex while nociceptive cutaneous afferents from the foot sole inhibited the ipsilateral but facilitated the contralateral peroneal reflex.

Inhibition of midbrain-evoked tonic and rhythmic motor activity by cutaneous stimulation in decerebrate cats

The effect of mechanical and electrical stimulation of cervical cutaneous afferents was analysed on both the centrally induced tonic and rhythmic activities in hindlimb antagonist muscle nerves of 16 decerebrate paralysed cats. Electrical stimulation of dorsal midbrain evoked in the nerve to the tibialis anterior muscle (TAn) either rhythmic discharges (n=14), associated with tonic discharges in ten cats, or only tonic discharges (n=4). Centrally induced activity in the ipsilateral nerve to gastrocnemius medialis (GMn) occurred in fewer cats (n=12) and displayed similar patterns as in TAn. Manual traction of the scruff of the neck reduced the TAn tonic and rhythmic discharges (n=6) by 73% (P<0.05) and 71% (P<0.05), respectively, and reduced only the tonic component of GMn discharges (by 41%, n=3). Electrical stimulation (impulses 0.1-0.5 ms, 50 Hz) of cervical nerves belonging to C5 or C6 dermatomes, the intensity (0.4-4 mA) of which induced minimal inhibition of both TAn and GMn discharges, reduced significantly the tonic component of TAn discharges (by 39%, n=4). At higher intensities of electrical cervical nerve stimulation (2-6 mA) inducing maximal inhibitory effect, both tonic and rhythmic activities in TAn and GMn were both significantly reduced by, respectively, 81% and 94% in TAn (n=7), and by 49% and 43% in GMn (n=7). Electrical cervical nerve stimulation consistently reduced the isolated tonic discharge in TAn by 66% (n=4, P<0.05) and in GMn by 23% (n=3) when present. Thus the tonic component was more sensitive to inhibition than the rhythmic component of hindlimb muscle nerve activity.

Causes of persistent postoperative headache after surgery for vestibular schwannoma

Our aim was to elucidate the aetiology of persistent postoperative headache, a common sequel for several years after vestibular schwannoma surgery through the retrosigmoid approach. Twenty-seven patients with reported major postoperative headache were tested for vestibular responses and cervico-collic reflexes. The role of local anaesthesia injected into the neck muscle insertions or around the occipital nerves was evaluated. Sixteen patients operated on for vestibular schwannoma, but without headache, and 12 healthy volunteers served as control groups. Vestibular responses and cervico-collic reflexes deteriorated equally in the patients regardless of whether or not they had a postoperative headache. Local anaesthesia did not alter the results. The posturography results were increased among both patient groups. Sumatriptan alleviated pain in nine patients and abolished it completely in one out of these nine patients. Vestibular imbalance or abnormal activation of neck muscles do not explain postoperative headache. Occipital nerve entrapment or neuralgia explains the headache in a few patients. The relatively pronounced sumatriptan effect may, however, suggest a trigeminal nerve mediated cause for postoperative headache.

Postural and symptomatic improvement after physiotherapy in patients with dizziness of suspected cervical origin

OBJECTIVE

To assess postural performance in patients with dizziness of suspected cervical origin in whom extracervical causes had been excluded, and to assess the effects of physiotherapy on postural performance and subjective complaints of neck pain and dizziness.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Primary care centers and a tertiary referral center.

PATIENTS AND SUBJECTS

Of 65 referrals, 43 patients were excluded because extracervical etiology was suspected. Of the remaining 22 patients, 17 completed the study (15 women, 2 men, x age 37 yr, range 26-49). The controls were 17 healthy subjects (15 women, 2 men, x age 36 yr, range 25-55).

INTERVENTION

Physiotherapy based on analysis of symptoms and findings, and aimed to reduce cervical discomfort. Patients were randomized either to receive immediate physiotherapy (n = 9), or to wait 2 months, undergo repeat measurements, and then receive physiotherapy (n = 8).

MAIN OUTCOME MEASURES

Posturography, measuring velocity and variance of vibration-induced body sway and variance of galvanically induced body sway. Subjective intensity of neck pain (Visual Analog Scale ratings, 0-100), intensity and frequency of dizziness (subjective score 0-4).

RESULTS

The patients manifested significantly poorer postural performance than did healthy subjects (.05 > p > .0001). Physiotherapy significantly reduced neck pain and intensity and the frequency of dizziness (p < .01), and significantly improved postural performance (.05 > p > .0007).

CONCLUSIONS

Patients with dizziness of suspected cervical origin are characterized by impaired postural performance. Physiotherapy reduces neck pain and dizziness and improves postural performance. Neck disorders should be considered when assessing patients complaining of dizziness, but alternative diagnoses are common.

Vestibular and somatosensory contributions to responses to head and body displacements in stance

The relative contribution of vestibular and somatosensory information to triggering postural responses to external body displacements may depend on the task and on the availability of sensory information in each system. To separate the contribution of vestibular and neck mechanisms to the stabilization of upright stance from that of lower body somatosensory mechanisms, responses to displacements of the head alone were compared with responses to displacements of the head and body, in both healthy subjects and in patients with profound bilateral vestibular loss. Head displacements were induced by translating two 1-kg weights suspended on either side of the head at the level of the mastoid bone, and body displacements were induced translating the support surface. Head displacements resulted in maximum forward and backward head accelerations similar to those resulting from body displacements, but were not accompanied by significant center of body mass, ankle, knee, or hip motions. We tested the effect of disrupting somatosensory information from the legs on postural responses to head or body displacements by sway-referencing the support surface. The subjects' eyes were closed during all testing to eliminate the effects of vision. Results showed that head displacements alone can trigger medium latency (48-84 ms) responses in the same leg and trunk muscles as body displacements. Nevertheless, it is unlikely that vestibular signals alone normally trigger directionally specific postural responses to support surface translations in standing humans because: (1) initial head accelerations resulting from body and head displacements were in opposite directions, but were associated with activation of the same leg and trunk postural muscles; (2) muscle responses to displacements of the head alone were only one third of the amplitude of responses to body displacements with equivalent maximum head accelerations; and (3) patients with profound bilateral vestibular loss showed patterns and latencies of leg and trunk muscle responses to body displacements similar to those of healthy subjects. Altering somatosensory information, by sway-referencing the support surface, increased the amplitude of ankle muscle activation to head displacements and reduced the amplitude of ankle muscle activation to body displacements, suggesting context-specific reweighting of vestibular and somatosensory inputs for posture. In contrast to responses to body displacements, responses to direct head displacements appear to depend upon a vestibulospinal trigger, since trunk and leg muscle responses to head displacements were absent in patients who had lost vestibular function as adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Central distribution of cervical primary afferents in the rat, with emphasis on proprioceptive projections to vestibular, perihypoglossal, and upper thoracic spinal nuclei

The projections of primary afferents from rostral cervical segments to the brainstem and the spinal cord of the rat were investigated by using anterograde and transganglionic transport techniques. Projections from whole spinal ganglia were compared with those from single nerves carrying only exteroceptive or proprioceptive fibers. Injections of horseradish peroxidase (HRP) or wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) were performed into dorsal root ganglia C2, C3, and C4. Free HRP was applied to the cut dorsal rami C2 and C3, greater occipital nerve, sternomastoid nerve, and to the C1/2 anastomosis, which contains afferents from suboccipital muscles and the atlanto-occipital joint. WGA-HRP injections into ganglia C7 and L5 were performed for comparative purposes. Injections of WGA-HRP or free HRP into rostral cervical dorsal root ganglia and HRP application to C2 and C3 dorsal rami produced labeling in dorsal and ventral horns at the level of entrance, the central cervical nucleus, and in external and main cuneate nuclei. From axons ascending to pontine and descending to upper thoracic spinal levels, medial collaterals were distributed to medial and descending vestibular, perihypoglossal and solitary nuclei, and the intermediate zone and Clarke's nucleus dorsalis in the spinal cord. Lateral collaterals projected mainly to the trigeminal subnucleus interpolaris and to lateral spinal laminae IV and V. Results from HRP application to single peripheral nerves indicated that medial collaterals were almost exclusively proprioceptive, whereas lateral collaterals were largely exteroceptive with a contribution from suboccipital proprioceptive fibers. WGA-HRP injections into dorsal root ganglia C7 and L5 failed to produce significant labeling within vestibular and periphypoglossal nuclei, although they demonstrated classical projection sites within the brainstem and spinal cord. The consistent collateralisation pattern of rostral cervical afferents along their whole rostrocaudal course enables them to contact a variety of precerebellar, vestibulospinal, and preoculomotor neurons. These connections reflect the well-known significance of proprioceptive neck afferents for the control of posture, head position, and eye movements.

The influence of initial posture on the sit-to-stand movement

Head movements, ground reaction forces and electromyographic activity of selected muscles were recorded simultaneously from two subjects as they performed the sit-to-stand manouevre under a variety of conditions. The influence of initial leg posture on the magnitude of the various parameters under investigation was examined first. A preferred initial leg posture resulted in smaller magnitudes of head movement and ground reaction forces. EMG activity in some muscles, trapezius and erector spinae, decreased, while in others, quadriceps and hamstrings, it increased in the preferred leg posture. The decreases seen correlate with reductions in head movement observed. The effect of inhibiting habitual postural adjustments of the head and neck, by comparing "free" and "guided" movements was also examined. In guided movements there are significant reductions in head movement, ground reaction forces and EMG activity in trapezius, sternomastoid and erector spinae. It would appear that both initial leg posture and the abolition of habitual postural adjustment have a profound influence on the efficiency of the sit-to-stand manouevre. This preliminary study high-lights the practical importance of head posture in the diagnosis and treatment of movement disorders, as well as in movement education.

Proprioception in the neck

Proprioception in the neck was investigated in normal human subjects. Three experiments studied rotation of the head about a vertical axis on the body. Accuracy of pointing, thresholds for detection of passive movement, and control of fine movement were tested. Comparison of the accuracy of pointing at the big toe with the nose and with the arm, showed a smaller scatter of angular misalignments when pointing with the arm. However, the arm pointed systematically off target. Pointing at the target toe by turning the head was not significantly more accurate than aligning the nose and toe by turning the chair and body with the head fixed. The highest threshold found for the detection of the direction of passive movement of the head relative to the body was 1.4 degrees angular displacement. Thresholds were highest at the slowest angular velocity and dropped as angular velocity increased. When the head was turned on the body thresholds were lower than when the body was turned and the head held still. Control of fine angular movements of the head and of the distal phalanx of the right thumb were compared by measuring subjects' accuracy in guiding a cursor through a path on a computer screen by turning the head or moving the thumb. The thumb was found to be better controlled than the head.

Organization of segmental input from neck muscles to the external cuneate nucleus of the cat

The musculotopic organisation of projections to the external cuneate nucleus (ECN) from the neck muscles splenius (SP) and biventer cervicis (BC) was examined electrophysiologically. These muscles are divided into a number of serially arranged compartments and are supplied by nerves from different cervical segments. About one-third of ECN neurons receive input from a single nerve. The majority of ECN neurons, however, receive input from more than one nerve in each muscle. ECN neurons are also limited in their ability to follow high frequency nerve stimulation and they frequently exhibit non-linear following. The connections and characteristics of ECN neurons suggest that a minority of neurons in the nucleus have the potential for the faithful transmission of afferent signals, but the majority have the potential to transform incoming patterns of muscle receptor discharge.

Organization of spinal inputs to the perihypoglossal complex in the cat

First- and second-order spinal afferents to the perihypoglossal complex were sought by using axonal transport of WGA-HRP. Injections in C1, 2, and 3 dorsal root ganglia resulted in axonal labeling in the nucleus intercalatus and the external cuneate nucleus, with a number of retrogradely labeled cells seen as well in the latter. A similar pattern of axonal labeling in the nucleus intercalatus as well as several retrogradely labeled cells were found after spinal cord injections at levels C1, 2, and 3. A prominent field of labeled axons was also present in the rostral main cuneate nucleus. No labeling was seen in the perihypoglossal nuclei after injections in the spinal cord or dorsal root ganglia at levels caudal to C3. After injections of HRP into the perihypoglossal nucleus we were able to identify labeled neurons within Rexed's laminae V-VIII and the central cervical nucleus. Anterograde labeling in the main cuneate nucleus was observed after C1 to C5 ganglion and C1 to C6 cord injections. The pattern and extent of labeling in the perihypoglossal nuclei and adjacent structures seen after cerebellar injections into lobules V and VI were comparable to those previously reported and permitted evaluation of the relay from dorsal root ganglia through the intercalatus to the vermis. Topography of the cervical projections to the nucleus intercalatus is considered with respect to that of the perihypoglossal-collicular projection. A discussion is offered of the apparent importance of nucleus intercalatus as a relay of cervical and vestibular afferent information to premotor structures involved in neck motor control. The perihypoglossal complex is viewed as being organized in such a fashion as to allow the nuclei intercalatus and prepositus hypoglossi to function as key structures in the integration of inputs related to neck and ocular motor control, respectively.

Patterns of primary afferent termination in the external cuneate nucleus from cervical axial muscles in the cat

Using the method of transganglionic transport of horseradish peroxidase (HRP), the distribution of primary afferent projections was examined in the external cuneate nucleus (ECN) from different muscle groups in the forequarter of the cat. The terminal zones of afferent fibers from three shoulder muscles--clavotrapezius, acromiotrapezius, and spinotrapezius--were compared to projections from suboccipital muscles, dorsal neck extensors, and muscles of the proximal forelimb. Each muscle group had a labelled terminal zone that occupied a different subvolume of the ECN. The zone labelled from trapezius muscles formed a continuous column in the ECN running from the caudal pole of the nucleus to a level 3.0 mm rostral to the obex. Terminal zones of suboccipital muscles and dorsal neck extensors formed longer columns that extended into the most rostral tip of the ECN, while those of proximal forelimb muscles formed shorter columns confined to the caudal two-thirds of the ECN. At comparable cross-sectional levels in the caudal and middle portions of the ECN, terminal zones from proximal limb muscles were located most dorsomedially, while those from shoulder muscles, dorsal neck muscles, and suboccipital muscles were located in progressively more ventral and lateral regions. The subvolume of the ECN occupied by projections from cervical axial muscles was estimated to be more than 40% of the volume of the nucleus, suggesting that the ECN has a major role in the transmission of sensory information from axial musculature to the cerebellum. Following exposure of all muscle nerves to tracer, a second labelled zone was also identified close to the ECN in the descending vestibular nucleus at transverse levels 2.0-3.0 mm rostral to the obex. Here, reaction product was concentrated around a circumscribed collection of medium-sized, multipolar cells.

Projections from C2 and C3 nerves supplying muscles and skin of the cat neck: a study using transganglionic transport of horseradish peroxidase

Transganglionic transport of HRP has been used to trace the pathways and termination sites of cutaneous and muscle afferent axons entering from the C2 and C3 dorsal rami. The muscle afferent projection in the spinal cord is restricted and (apart from the ventral horn) largely confined to the intermediate gray matter. There is a muscle afferent projection to the ventrolateral main cuneate nucleus and a complex pattern of projection through the extent of the external cuneate nucleus. In contrast, the cutaneous spinal projection is abundant with extensive filling of axons in the tract of Lissauer and many termination sites in the lateral substantia gelatinosa. Axons enter the lateral gray matter of the cervical spinal cord from the dorsal columns and the dorsolateral funiculus and terminate in the lateral one-third of the dorsal horn as far rostral as the spinomedullary junction. Axons of the tract of Lissauer form a complex web around the dorsal horn and many penetrate rostrally to the region of the spinomedullary junction, where they terminate among clusters of interstitial cells on and close to the dorsal medullary surface. Cutaneous afferent axons from the dorsal columns turn into the main cuneate nucleus and enter a dense mass of HRP-reaction product which occupies the most ventrolateral part of the nucleus for its entire length.

Reflex effects from high threshold neck muscle afferents on hind limb extensor gamma motoneurones in the cat

The supra-segmental control of hind limb gamma motoneurones from neck muscle receptors has been studied in decerebrated and in spinal cats. Stretch of individual dorsal neck muscles was not an adequate stimulus for evoking long spinal reflexes to gamma motoneurones of gastrocnemius-soleus (GS) muscles unless the stretch was maximal or excessive. Pressure applied to the neck muscles, or intramuscular injections of KCl solution (0.1 ml, 5%), did affect the discharge of GS gamma motoneurones. Excitation was more evident than inhibition. We conclude that the long spinal reflex effects originate from high threshold mechanoreceptors, or nociceptors, rather than muscle spindles.

Postural effects of neck muscle vibration in man

Vibration of the dorsal neck muscles in man induces falling reactions, walking and "marche en étoile", probably by muscle afferent activation. It can be used as a reproducible error signal in analyzing the interaction between neck muscle proprioception and vestibular as well as ocular motor systems. These interactions are important for posture and coordinated head-eye movements.

Propriospinal fibers interconnecting the spinal enlargements in some quadrupedal reptiles

The cells of origin, course and site of termination of long propriospinal fibers interconnecting the intumescences have been studied with the aid of the horseradish peroxidase technique, as well as with anterograde degeneration techniques, in some quadrupedal reptiles (the lizards Tupinambis nigropunctatus and Varanus exanthematicus, and the turtles Testudo hermanni and Pseudemys scripta elegans). The anterograde degeneration findings suggest that long descending propriospinal fibers from the cervical intumescence are distributed bilaterally to the ventral gray of the lumbar enlargement, including the lateral motoneuron column. Long ascending fibers from the lumbar to the cervical intumescence are distributed, also bilaterally, to the ventromedial part of area VII--VIII. The cells of origin of long descending propriospinal fibers wre found in the medial part of area VII--VIII in the cervical intumescence, particularly contralateral to the injection side. The cells of origin of long ascending propriospinal fibers were found in the lumbar intumescence, also particularly contralateral to the injection side, in the ventromedial part of area VII--VIII. It seems likely that in the reptiles studied the long propriospinal fibers interconnecting the spinal enlargements are in large part organized as crossed connections. The demonstration of long propriospinal fibers in lizards and turtles--i.e. quadrupedal reptiles that move their limbs in a particular diagonal pattern--suggests that these pathways are of great importance for the coordination of forelimb and hindlimb movements.

The location of spinal neurons with long descending axons (long descending propriospinal tract neurons) in the cat: a study with the horseradish peroxidase technique

The distribution spinal neurons with long descending axons was studied in the cat by means of retrograde transport of horseradish peroxidase. Labeled neurons appeared bilaterally in the cervical and the thoracic cord following injections in the lumbosacral cord. In some cases hemisections were made rostrally and contralaterally to the injections in an attempt to determine whether or not the axons crossed. Neurons with uncrossed descending axons were located in laminae I, V, VII and VIII. Lamina I neurons were present in all the spinal segments. In lamina V labeled neurons were distributed mainly laterally in the cervical cord but medially and laterally in the thoracic cord. In the upper cervical and the thoracic cord laminae VII and VIII neurons were distributed very densely along the lateral cord, accounting for 30 and 40 of the total labeled neurons, respectively. In the cervical enlargement they were located in the middle part of lamina VII and in lamina VIII, accounting for about 25% of the total labeled neurons. Neurons with crossed descending axons were found in laminae V, VII and VIII, in the medial part of lamina VII including the intermediomedial nucleus of the thoracic levels and close to the central canal. Lamina V neurons were very small in number. The largest collections of labeled neurons were present in the medial part of laminae VII and VIII. They accounted for about 45% to 55% and 37% of the total in the cervical and the thoracic cord. These neurons may function as the long spinal reflex paths for forelimb-hindlimb synergies and the intercalated paths between the supraspinal descending tracts and the spinal motor centers.

Effects of postural changes of the upper limb on reflex transmission in the lower limb. Cervicolumbar reflex interactions in man

The influence of passive changes in upper limb position on the excitability of three myotatic arc reflexes (soleus, quadriceps, and biceps femoris) of the lower limb has been explored on 42 volunteers. The results indicate that the excitability of the three myotatic arcs can be influenced at a distance by postural modifications of the upper limb. When the ipsilateral upper limb is forwards or the contralateral backwards, a facilitation of both soleus and quadriceps tendon reflexes is observed while the biceps femoris reflexes are reduced. This pattern of facilitation and inhibition is reversed when the ipsilateral upper limb is backwards or the contralateral forwards. The facilitations as well as inhibitions of proximal myotatic arc reflexes are quantitatively more marked than that of the soleus reflex. Facilitation and inhibition are not linearly related to the angle of the arm with the trunk. Effects begin at a considerable angle, become maximal at 45 degrees, and progressively disappear for greater values. It is suggested that the distinct pattern of facilitation and inhibition which is exerted in reciprocal fashion on extensor and flexor motor nuclei might depend on the long propriospinal neurones connecting cervical and lumbar enlargements.

Cortical and long spinal actions on lumbosacral motoneurones in the cat

1. The effects of stimulating forelimb afferents on various ipsilateral motoneurones of the hind limb have been compared with those of volleys set up in the contralateral pericruciate cortex in cats anaesthetized with chloralose. 2. With intact neuraxis, brachial plexus volleys evoke discharge of flexor and extensor motoneurones; short cortical tetani also elicit discharge mainly of flexor motoneurons. After a pyramid-sparing brainstem lesion, little or no firing is evoked by either input. 3. Monosynaptic reflex testing and intracellular recording reveal subthreshold actions on hind-limb motoneurones, inhibition of FDHL and later facilitation of extensors and flexors by forelimb volleys, facilitation of flexors and extensors together with inconstant inhibition of the latter, by cortical stimulation. 4. Interruption of medullary extrapyramidal paths greatly reduces intensity and duration of facilitation from the forelimb, and largely removes cortically evoked extensor facilitation. Inhibition of FDHL from forelimb and cortex is unchanged; cortical volleys continue to facilitate flexors, and have mainly inhibitory action on extensors in these 'pyramidal' preparations. 5. Hyperpolarization of FDHL motoneurones occurs in response to forelimb and cortical volleys, of time course corresponding to depression of test reflexes. Spinal pathways responsible for the two inhibitory actions are independent, and unless each is very strong, their separate actions summate when elicited together. 6. Receptive field for FDHL inhibition from the forelimb is located distally in the forepaw, and its receptors are largely served by cutaneous fibres of low threshold; some Group II fibres in distal muscle nerves also contribute. Receptive field for facilitation embraces the whole limb, and the executant afferent fibres are of higher threshold. 7. Natural stimulation of the forelimb can evoke the long spinal actions, vibration or light pressure on the forepaw eliciting FDHL inhibition, and strong pinching evoking the more general facilitation. Possible functional roles of these actions in the intact animal are discussed.

Spino-spinal mechanisms in the chloralose anaesthetized cat

1. In chloralose anaesthetized cats the events in the lumbosacral cord that follow stimulation of a forepaw or neck nerve have been examined.2. Four events take place in the lumbosacral cord after forepaw or neck muscle nerve stimulation. These are: (1) a brief period of generalized enhanced motoneurone excitability, (2) a prolonged and as yet unexplained enhancement of monosynaptic reflexes, (3) a period of presynaptic inhibition in muscle and skin afferent fibres, and (4) a prolonged inhibition of spino-bulbo-spinal reflexes.3. A variable and sometimes selective reduction of one or another descending effects follows the placing of small lesions in the anterior portion of the suprasylvian gyrus.

Cervico-lumbar reflex interactions involving a proprioceptive receiving area of the cerebral cortex

1. In the decerebrate cat descending cervico-lumbar reflex interactions from neck muscle nerves are absent, and those from forepaw nerves are reduced or absent.2. Lesions restricted to the anterior pole of the suprasylvian gyrus regularly abolish descending cervico-lumbar reflex interactions from neck muscle nerves. The same lesions may reduce or abolish descending cervico-lumbar reflex interactions from forepaw nerves.3. The ascending cortical looping pathway utilized in descending cervico-lumbar reflex interactions is crossed, and the descending pathway from the cerebral cortex is bilateral.