Diagram illustrating some neuronal relationships in Clarke's column described by Rethelyi 658. Although additional components have been described since this work was published, this figure demonstrates some fundamental relationships among the neuronal elements in this nucleus. Notice particularly extensive interconnections between the primary afferents (P. aff.) and the large focal cells (FC). DSCTa, axon of focal cell comprising the fibers of the dorsal spinocerebellar tract; Rec. coll., recurrent collateral of focal cell axons; BC, border cell; BCa, axon of the border cell.

Relationship between discharge frequency of dorsal spinocerebellar tract (DSCT) neurons and extension of the muscle in cats anesthetized with pentobarbital. Ordinate: mean frequency of firing in the period 0.5–1.5 s after end of dynamic stretch. Abscissa: length of muscle extension. A: gastrocnemius‐soleus units. B: tibialis anterior‐extensor digitorum longus units. Each symbol indicates data from a single DSCT neuron.

Demonstration of linearity of responses of some DSCT neurons using linear systems analysis. This figure shows a plot of the gain of the response

Examples of types 2 and 3 responses recorded from dorsal spinocerebellar tract neurons in cats anesthetized with pentobarbital. A–C: examples of type 2 responses. Each shows an initial decrease in impulse density. D–F: examples of type 3 responses. These show a peak impulse density that is wider, smaller, and usually with a longer latency than observed for responses to monosynaptic inputs (type 1) described by these authors.

Proprioceptive subdivision of Clarke's column. This diagram depicts some of the known patterns of convergence occurring in this subdivision. The interneuronal systems are hypothetical and have been included only to indicate patterns of convergence from peripheral afferents onto projection neurons in this nucleus. Cells whose axons comprise the dorsal spinocerebellar tract (PC) actually include all three types of neurons in Clarke's column (see text). In this diagram monosynaptic convergence of group Ia, Ib, and group II afferents onto single neurons has been excluded for simplicity. Although their physiological action is hypothetical, the recurrent collaterals of projecting neurons are included. PC, projection cells; •, excitatory interneurons; ○, inhibitory interneurons; ⊗, neurons mediating presynaptic inhibitory interactions; PT, pyramidal tract.

Cutaneous subdivision of Clarke's column. This diagram depicts many of the neuronal interconnections underlying the patterns of convergence which have been described in this part of the nucleus dorsalis. PC, neurons projecting in the dorsal spinocerebellar tract; ○, excitatory interneurons; •. inhibitory interneurons; ⊗, neurons mediating presynaptic inhibition. Cutaneous (R), rapidly adapting afferents from the skin; cutaneous (S), slowly adapting afferents from skin; FRA, other flexor reflex afferents; PT, pyramidal tract; Ret. S, reticulospinal system; Raphe S, raphe‐spinal projection.

Action of some descending pathways on segmental interneurons and cells of origin of the ventral spinocerebellar tract (VSCT). A: organization of input from the vestibulospinal tract (VST) and the proposed input from the pyramidal tract (PT) to the Ia inhibitory interneuron (filled neuron) and spinal border cells (SBC). B: organization of inputs from the rubrospinal tract (RST) and pyramidal tract to Ib inhibitory interneurons (filled neuron) and spinal border cells. Note that inputs from any of these pathways into inhibitory interneurons and spinal border cells are similar. Interneurons affecting the activity of spinal border cells also exert similar effects on α‐motoneurons (MN).

Diagram showing relationships between Ia inhibitory interneurons (•), Renshaw cells (R), α‐motoneurons innervating synergistic (sMN) and antagonistic (aMN) muscles, and the cells of origin of the ventral spinocerebellar tract (VSCT). Notice that some VSCT neurons mediate action of Renshaw cells, whereas others are affected principally by Ia inhibitory interneurons.

Input to spinal border cells and motoneurons from flexor reflex afferents and the organization of the inputs from some descending pathways to this system. Note the parallel arrangement of spinal border cells (SRBCs) and motoneurons (MN). FRAc and FRAp, flexor reflex afferents from the center and periphery of the receptive fields, respectively; CN, extrapyramidal pathway from cerebral cortex; PT, pyramidal tract; Ret Sp, reticulospinal pathways.

Sites of origin of several spinocerebellar projections in cats and the distribution of their fibers. Crossed pathways originate in 1) central cervical nucleus (CCN), 2) lamina VII from sixth lumbar nerve, L₆, caudally, 3) lamina VIII from the cervical to lumbar cord, 4) spinal border cells (SBC), 5) dorsal horn of sacral and caudal segments, and 6) laminae VII and VIII of the sacral and caudal segments. Uncrossed pathways originate from 7) lamina VI in the cervical cord, 8) lamina VII at C₆‐T₁, 9) lamina V in the lower cervical to lumbar cord, 10) Clarke's column (CC), and 11) lamina VI at L₅ and L₆. UC, upper cervical; CE, cervical enlargement; T, thoracic; LE, lumbar enlargement; S, sacral; Ca, caudal.

Organization of the pontine projection to the anterior lobe in cats. Vermal projection is indicated by ○ (lobules I–IV) and • (lobule V). The projection is bilateral, and cells projecting to rostral lobuli are located more dorsally than those projecting to caudal lobuli. The intermediate‐lateral part receives fibers principally from medial and lateral groups of cells located contralaterally (hatching). Caudally the lateral area coincides with the region of the nuclei projecting to the vermis, and there is a topographic correspondence of the inputs to the vermis and intermediate cortex. The topographic pattern of inputs from the medial pontine nucleus is reversed and is not as well defined.

Pontocerebellar projection to the posterior lobe in cats. Sections are equally spaced through the pons from rostral (X) to caudal (I). On the right, the distribution of labeled cells following injections in lobules VI–VIII is indicated by different symbols shown in the diagram of these lobules below and to the left. On the left of the pontine sections, the sites corresponding to the 4 columns of pontine neurons (A–D) are indicated. The diagram below and to the right shows the longitudinal extern of the columns and the regions that project to lobules VI–VIII, respectively. Quantitative differences in projections to the various lobules are not indicated but can be seen on the right of the transverse drawings of the pons (above). N.dl., dorsolateral pontine nucleus; N.I., lateral pontine nucleus; N.m., medial pontine nucleus; N.p., peduncular pontine nucleus; N.pm., paramedian pontine nucleus; N.v., ventral pontine nucleus.

Summary of areas of termination within the pontine nuclei from the 2nd and 1st somatosensory areas (SII, SI) and the motor area (MI) on the cat cerebral cortex. Longitudinal pontine columns projected on by SII, SI, and MI are presented on each side of the drawing of a transverse section through the lower part of the pons. Note the organization of somatotopical projections. The SII and SI project to the same medial column; otherwise SII, SI, and MI project to different areas.

Projections from the 3 subdivisions of the paramedian reticular nucleus (PRN) onto parts of the cerebellar cortex and nuclei in cats. Variations in the density of symbols indicate relative densities of projections from the 3 subdivisions to the different cerebellar areas. N.l., nucleus lateralis; N.i.a., nucleus interpositus anterior; N.i.p. nucleus interpositus posterior; N.f., nucleus fastigii; L.pm., paramedian lobule; P.fl.d., dorsal paraflocculus; P.fl.v., ventral paraflocculus; Flocc., flocculus; Cr. I, crus I; Cr. II, crus II; L. simpl., lobulus simplex; l. ans., lobulus ansiformis.

Topographical projection from the lateral reticular nucleus (NRL) on to the paramedian lobule and the anterior lobe in cats. Four representative transverse sections through the left NRL are shown on left. Symbols depicting the sites of origin of each projection correspond to symbols labeling their areas of termination in the cerebellum. The anterior lobe (vertical and oblique hatchings) receives afferents from more ventral parts of NRL than does paramedian lobule (• and ○), although there is extensive overlap. Furthermore the “hindlimb” areas within the anterior lobe (vertical hatching) and the paramedian lobule (○) are connected mainly with lateral (parvocellular) part of the NRL, while the cerebellar “forelimb” areas (oblique hatching and •, respectively) mainly receive afferents from the medial or magnocellular part of the NRL. The projection from the subtrigeminal part to the anterior lobe and paramedian lobule is not illustrated. Lob. paramed., paramedian lobule.

Organization of spinal inputs to the lateral reticular nucleus (LRN). This diagram shows: 1) organization of the input from the bilateral ventral flexor reflex tract (bVFRT) to the LRN and 2) organization of descending pathways to this ascending projection. Note the relationship between the direct spinocerebellar afferent pathways (SAP) and the reticulocerebellar projection from LRN. PT, pyramidal tract; Ret SP, reticulospinal pathways; FRAc and FRAp, flexor reflex afferents from center and periphery of receptive fields, respectively; MN, α‐motoneuron; ICP, inferior cerebellar peduncle.

Effect of spinal lesions on responses of neurons in the lateral reticular nucleus (LRN) to peripheral nerve stimulation in cats anesthetized with α‐chloralose. Responses in B and C were obtained from two types of LRN neurons following the stimulation of the hamstring nerve (HN) at a strength just great enough to evoke a group I volley in an exposed dorsal root. These responses were obtained in an animal with a lesion at the midthoracic level that severed all but the ipsilateral dorsolateral funiculus (A). In another preparation all but the ventral quadrant was sectioned (D). Under these conditions the isolated LRN neuron did not respond when only group I peripheral afferents were activated (E). When stimulus intensity was great enough to activate high‐threshold muscle afferents (F), the neuron responded.

Convergence from cortical and spinal inputs onto a cell in the lateral reticular nucleus in a decerebrate cat anesthetized with nitrous oxide. A–H: poststimulus time histograms (PSTH) and plots of the cumulative frequency distribution (CFD) obtained by averaging 64 responses to stimulation of peripheral nerves (A, E), forelimb (C, D), and hindlimb (G, H) areas of the sensorimotor cortex and mechanical tapping (0.8‐mm amplitude, 17‐ms duration) of forelimb central foot pad (B) and hindlimb central foot pad (F). Time scale is indicated in B. Calibration bars in A apply to all records except the CFDs in B and F. In all records, onset of stimulus is indicated by vertical bar. iSR, ipsilateral superficial radial; FCP, forelimb central foot pad; ASG, anterior sigmoid gyrus; PSG, posterior sigmoid gyrus; iSCI, ipsilateral sciatic nerve; HCP, hindlimb central pad; 10 T, 10 times threshold.

Relationship between the lateral reticular nucleus (LRN), fastigial nucleus (FN), Deiters' nucleus (DN), and the bilateral ventral flexor reflex tract (bVFRT). VIII, vestibular nerve; αMN, α‐motoneuron.

Distribution of several projections to the lateral reticular nucleus in cats. To the left, the distribution of inputs is shown on a horizontal section through the brain stem. To the right, they are presented in transverse sections at levels B and C. Note the overlap of afferents from different sources.

Topographical relations of inputs from several sources to the nucleus reticularis tegmenti pontis (Nrt) in the cat. A: in the top 2 drawings, the cortical areas with and without projections to the Nrt are indicated by the dots and dashes, respectively. White parts indicate areas where projections have not been studied. Below, a series of transverse sections through the Nrt shows the sites of termination (dotted) of fibers from the cerebral cortex. B: diagram illustrating the preferential distribution of fibers within this nucleus from specific cortical regions. Note the topographic arrangement (with considerable overlap) in the projections of anterior sigmoid (S.a.) and posterior sigmoid (S.p.) gyrus. C: diagram showing the main distribution in the Nrt of afferents from other sources and their relationship to inputs from the cerebral cortex. Pr., proreate gyrus; Orb., orbital gyrus; Co., coronal gyrus; E.a., anterior ectosylvian gyrus.

Intracellular recording of the responses of a dentate neuron to stimulation of the cerebellar surface (CbS) and the decussation of the brachium conjunctivum (BC). Responses of this neuron before and after penetration are illustrated in parts A and B, respectively. The IS‐SD (initial segment‐soma dendritic) break of the action potentials evoked by these stimuli was particularly apparent when the spike‐generating mechanism began to deteriorate (C). When the spikes could no longer be evoked, a graded hyperpolarization was observed in response to CbS stimulation (D and E). The records in F were obtained just outside this cell (three superimposed traces). The stimulus strength of the CbS stimulus was the same in A–D.

Neurons in the interposed nucleus giving rise to nucleocortical fibers. A: neuron in the medial part of nucleus interpositus anterior reconstructed from 14 frontal sections. The nucleocortical collateral passes almost directly rostral to the soma, a₁: Antidromic responses of the neuron in A following stimulation of the brachium conjunctivum. a₂: Synaptic responses of this neuron after stimulation of inferior olive. Voltage calibration is 10 mV for a₁ and 20 mV for a₂. Time calibration is 2 ms for a₁ and 20 ms for a₂. Arrows indicate the time of stimulus onset. B: neuron in A drawn at a lower magnification showing its position in frontal section. C: neuron located in the nucleus interpositus posterior (NIP), which appeared to give rise to a nucleocortical collateral. Reconstructed from 6 sagittal sections. c.: synaptic response of this neuron following stimulation of the inferior olive. Calibrations are 5 mV and 10 ms. D: drawing of the neuron in C at a lower magnification showing its position in the NIP and the dorsolateral trajectory of a possible nucleocortical collateral. Calibration in A also applies to C, and calibration in B applies to D.

A: low‐power light‐field photomicrograph of a transverse section through the cerebellum. B: dark‐field photomicrograph of outlined area of the cortex in A showing labeled nucleocortical fibers (arrows) that have coursed dorsorostrally from the injection site in the fastigial nucleus into the corpus medullare of the anterior lobe. Calibration, 200 μm.

Configuration, nomenclature, and diagrammatic representation of the olive. Upper part of figure shows a series of 15 standard tranverse planes through the inferior olive. Different symbols illustrate the extent of the main olivary subdivisions, and subgroups of the olive are identified by lettering. Below, a diagrammatic illustration of the inferior olive is represented unfolded and viewed in the horizontal plane with all levels superimposed. Interrupted numbered lines indicate position of the levels of the transverse planes in this reconstruction, and the main cellular groups and subgroups are indicated. On the bottom of the figure, the transformation of the olive into a flat structure is described for a chosen transverse level. DAO, dorsal accessory olive; dc, dorsal cap; dl, dorsal lamella of principal olive; dmcc, dorsomedial cell column; MAO, medial accessory olive; PO, principal olive; vl, ventral lamella of principal olive; vlo, ventrolateral outgrowth; β, subnucleus β.

Summary of afferent projections to the olive on 5 diagrammatic representations of this nucleus. All major regions projecting to the olive are indicated. Symbols illustrate the correspondence of afferent projections and specific nuclei or regions within the olive.

Olivocerebellar projection. On upper left, a diagrammatic representation of the unfolded cat cerebellum. Different regions of the cerebellar cortex are identified with each diagrammatic representation of the olive. Symbols identify regions of the olive and the portions of the cortex where they send their projections. On the upper right, outlines of the cerebellar nuclei along with the lateral vestibular nucleus are shown in the horizontal plane. Immediately underneath, in diagrammatic representation of the olive, symbols identify regions projecting to these nuclei.

Schematic representation of the unfolded cerebellum summarizing the general distribution of the olivocerebellar projection (left) and the contribution from individual subgroups and regions of the olive (right). Oblique lines in drawings of the cerebellum and unfolded olive (below) correspond to the caudal third of the olive, vertical lines to the middle third, and horizontal lines to the rostral third. Cross‐hatching in cortex corresponds to areas receiving projections from the middle and rostral thirds of olive.

Corticonuclear projection. Diagrammatic representation of the unfolded cerebellum. Symbols indicate position and relative size of cerebellar cortical regions projecting to the intracerebellar nuclei and lateral vestibular nucleus. Roman numerals indicate the vermian lobules. Cr. I, crus I; Cr. II, crus II; Flocc., flocculus; L.pm., lobulus paramedianus; L. simpl., lobulus simplex; P.fl.d., paraflocculus dorsalis; P.fl.v., paraflocculus ventralis.

The first records of action potentials recorded intracellularly from olivary neurons in cats. Upper record: response to stimulating the cerebral cortex (CO); lower record: response to antidromic activation of the neuron by stimulating the cerebellum (CB). Arrows indicate inflections frequently observed on prolonged depolarization.

Demonstration of electrotonic coupling between inferior olivary neurons in cats. A: intracellular recording from an olivary cell responding to an antidromic stimulus that straddled threshold (middle trace). When no action potential was evoked in the neuron, short‐latency depolarizations (SLD) could be observed (lowest trace). Top trace is a reference trace to measure the resting potential of the cell. This cell had a resting potential of 50 mV and a spike amplitude of 70 mV. B: extracellular recording showing the field potential outside this neuron. C–F: intracellular records from another olivary cell. C: 3 types of responses to the antidromic stimulus: a full action potential, an initial segment (IS) spike, and SLD. Responses are shown on superimposed traces. D: record at fast‐sweep speed (lowest trace) showing the exact interval between the antidromic invasion and the SLD. D–F: The SLD could be graded by stimulation of the cerebellar white matter at increasing amplitudes. G: extracellular field potential recorded outside this neuron. Upper trace, extracellular reference potential; the middle trace, response recorded at low‐gain and slow‐sweep speed; and the lower trace, response recorded at high‐gain and fast‐sweep speed.

Plexus of noradrenergic fibers found in all cortical layers of the chicken cerebellum. In the granular layer, the fibers have a predominantly sagittal orientation and form a netlike plexus. Radially oriented branches pass through the Purkinje cell layer and bifurcate to form longitudinally oriented fibers in the molecular layer. In the white matter the fibers appear to be distributed in sagittal zones, but this feature could not be demonstrated unequivocally (question, mark). In the inset the branching pattern of the Purkinje cell dendrites are represented schematically for comparison with the pattern of fluorescent fibers in the corresponding areas of the molecular layer.

The distribution of the serotonergic, afferent axons within the cerebellar cortex and the cerebellar nuclei of the rat. In the cortex of the flocculus, paraflocculus, and lateral hemisphere (right), axons containing serotonin 1 form 1% of the mossy fiber rosettes in the granular layer. Other serotonin‐containing axons branch diffusely 2 and distribute in the granular and molecular layers. A third type 3 of axon containing serotonin bifurcates in the molecular layer and forms elements resembling parallel fibers. These axons constitute 0.1% of the fibers in this region. Collaterals from each of these 3 systems are present in deep cerebellar nuclei. These 3 types of afferents are also present in the vermal and paravermal cortex (left). In this region, however, there are fewer fibers forming rosettes 1. A diffuse‐branching varicose system 2 also exists, and the fibers forming parallel fiberlike axons 3 in the molecular layer are more numerous. These fibers constitute 0.5% of the fibers in the molecular layer. The collaterals of these 3 fibers project to the cerebellar nuclei. For comparison, the other 3 types of afferent fibers to the cerebellar cortex and nuclei are also illustrated: the mossy fiber (MF), the climbing fiber (CF), and the varicose branching system of catecholamine axons originating from the locus coeruleus (LC). Some of these fibers also bifurcate in the molecular layer like parallel fibers.

Response of a Purkinje cell to a proprioceptive stimulus in an awake, locally anesthetized cat. A: responses (poststimulus time histograms) to 7 randomly delivered stretches of the extensor digitorum communis muscle, each with a different slope (velocity). Vertical calibration: 400 μm (displacement signal) and 8 impulses/bin (histogram). Δ t is the time epoch over which change in firing rate is measured for plots in B. The relationship between Δ , the change in firing frequency, calculated during Δ t and velocity of stretch. Points were obtained from 5 different Purkinje cells, each from a different preparation. Each symbol indicates a different neuron. The line is the linear regression plot for these data.

Changes in simple spike activity (SS) and responses to climbing fibers (CS) recorded from four different Purkinje cells during movement of the wrist joint in an unanesthetized decerebrate cat. The responses consist of event histograms constructed from the number of consecutive responses shown in upper right of each record. In two cells shown in histograms B and C and histograms D and E, the frequency of the SS activity evoked by the stimulus in A was reduced after the occurrence of the response to the climbing fiber input. In G and H and also in I and K, two other cells responded with an increase in SS activity just before the response to climbing fibers was evoked near the end of the upward movement (stimulus shown in F). Notice that the response evoked by climbing fibers in B and D had very low thresholds. (ω, angular velocity). Abscissa in A and F is the angle of joint movement. Abscissa in B–E and G–K is counts per bin. Ordinates are calibrated in seconds.

Sensitivity of Purkinje cells to natural cutaneous stimuli in decerebrate unanesthetized cats. Poststimulus time histograms (left) and cumulative frequency distributions (right) were constructed from 64 consecutive responses of the cell to graded taps applied to the foot pad of toe 4 (T4). Amplitudes of stimuli are shown above each record. Short vertical bars indicate onset of stimulation.

Effects of stimulating several peripheral inputs on the activity of a dentate neuron in a monkey anesthetized with α‐chloralose. Histograms in A‐F were each obtained from 64 consecutive responses to stimuli applied at the location indicated under each record. Note convergence of inputs to this cell.

Effects of spinal cord lesions on the responses of a dentate neuron to stimulation of the spinal cord in a cat anesthetized with α‐chloralose. The histogram in A shows the control response of the neuron to stimulation of spinal cord. This response was abolished by a spinal cord lesion restricted to the dorsal columns (B). In C, the stimulating electrode was moved rostral to the lesion, and another control histogram was obtained. A subsequent lesion of the spinal cord that did not interrupt the dorsal column (D) produced no significant effect on the response of this dentate neuron to spinal cord stimulation. All histograms were constructed from 100 consecutive responses.

Specificity of Purkinje cell responses to stretch of extraocular muscles in a cat anesthetized with nitrous oxide. A: responses of cells to 64 stretches of the muscles acting in the vertical plane. B: responses of another cell to 128 stimuli to left and right lateral recti. Upper histogram of each pair in B is constructed from the simple spike activity, whereas the lower is constructed from the complex spike response to climbing fiber inputs. RIR, right inferior rectus; RSR, right superior rectus; LIR, left inferior rectus; LSR, left superior rectus; LLR, left lateral rectus; RLR, right lateral rectus.

Convergence patterns of inputs onto interposed neurons from 2 muscles, stretched individually and together, in an awake locally anesthetized cat. Neurons from 3 different cats are shown in A, B, and C. Bin width of poststimulus time histograms is 2 ms. Each histogram is constructed from 128 consecutive responses. EDC, extensor digitorum communis; PL, palmaris longus; BR, brachioradialis.

Response of climbing fiber inputs to flocculus activated by visual stimuli in rabbits anesthetized with α‐chloralose and urethane. A and B: extracellular recordings of the responses to climbing fibers recorded from an individual Purkinje cell in the nodulus. In A, the rising phase of the Purkinje cell response initiated the oscilloscope sweep. Multiple deflections (arrows) on the falling phase identify responses due to climbing fiber activation of the Purkinje cell. B: effect of the movement (0.5°/s) of a large contrastrich pattern on climbing fiber activity. The preferred direction was from posterior (P) to anterior (A). Movement of the pattern was preceded and followed by a control period during which the pattern was stationary. In C, the activity in B is presented in the CLOOGE format, in which the logarithm of successive response intervals is represented as a sequence of dots in time (e.g., the starred interval in B corresponds to the starred dot in C). D: poststimulus time histogram revealing the on‐off characteristics of the response to climbing fiber input in A–C. The unit showed only “on” activation. The ordinate represents total counts per 25‐ms bin for 75 stationary presentations of the pattern. Interval between projection periods was 5 s.

Response of a neuron in lobule VIIB to virtual sound source motion in an awake, locally anesthetized cat. A: response to virtual sound‐source motion. A 2‐s train of clicks was presented dichotically at progressively changing time delays ranging from 0–500 μs. Virtual sound movement is from the leading ear to the midline and back. Note that the neuron responded only with virtual sound motion in the direction from the leading ear to the midline (left half of A) and not in the opposite direction. B: response to stationary (virtually midline) source. Click trains were presented without any interaural time delay. C: no stimulation. The interaural delay is indicated in middle of each figure. Bin width, 32 ms. In A and B, the clicks are dichotically presented at a rate of 20/s. The sweep was triggered at the onset of each click train and lasted for the duration of the train. Histograms in A, B, and C were constructed from the sum of 20 sweeps. Intensity of stimuli in A and B: 58 dB sound pressure level.

Types of cerebellar Purkinje cell responses in a curarized frog to sinusoidal horizontal rotation. The average “simple” spike activity during 10 cycles of horizontal sinusoidal rotation are shown at 0.25 Hz ± 20° for types I–IV responses (A–D, respectively). The background frequency for each type (dashed line in A–D) was averaged during a 10‐s period prior to rotation. Stimulus insert (solid sinusoid) is head angular acceleration. Abscissa, portion of the stimulus cycle in degrees. Each bin equals 9°.

Cycle histograms of the responses of a neuron from the left fastigial nucleus to low‐frequency stimuli in awake unanesthetized monkeys. Histograms on left compare responses to horizontal sinusoidal stimuli of ± 20° amplitude applied in the normal seated position (horizontal) with responses to oscillations about the vertical axis when the nose was steadily tipped downward 20° (nose down) at 0.9 Hz. These responses are essentially identical in amplitude and phase. Histogram on lowest left (tilt) shows the unitary response to vertical tilt; this unit increased its firing rate in response to pitching the nose downward and decreased firing rate with nose‐upward movements. Mean phase lag of the unit response with respect to vertical tilt measured 66°. As indicated in histograms on the right, unit showed clear sinusoidal modulation of its firing patterns, even with horizontal stimulus frequencies as low as 0.2 Hz. Mean tonic firing rate in the horizontal position was 61 spikes/s. Total number of stimulus cycles in each histogram: 25 (0.9–0.5 Hz) or 20 (0.2 Hz). Sample bin width: 5 ms (0.9 Hz), 10 ms (0.5 Hz), or 25 ms (0.2 Hz).

Regulation of the vestibuloocular reflex (VOR) via the output of the flocculus. A: The output of Purkinje cells (P) is affected by a head‐velocity input (V_H) and an eye‐velocity input (V_E). The output of the Purkinje cells in turn regulates responses of brain stem neurons (VOR interneurons) that project to extraocular motor nuclei. B and C: vector representations of head velocity, eye velocity, and firing rates of neurons in A. Each line in B and C represents a different condition and shows how the output of the Purkinje cell (P) contributes to the resultant eye movement. Each vector indicating velocity represents eye movement relative to the monkey's moving head. These representations and diagram in A should be read from right to left. Notice that the vectors change direction at each inhibitory synapse. The abducens vector, which represents the velocity component of the response of abducens motoneurons, is in phase with eye velocity. In B, VOR indicates the vestibulo‐ocular reflex induced by head rotation of ± 10°. SP indicates smooth pursuit eye movement in the absence of head rotation. Suppression indicates suppression of the VOR. In C, ± 25° out and ± 13.5° out indicate that the eye movement was 180° out of phase when the head was rotated at 2.5 and 1.35× head velocity, respectively. Similarly, ± 12.5 in means that eye movement was in phase with head rotation at 1.25× head velocity.

Synaptic input to neurons in nucleus prepositus hypoglossi (ph) and correlation of their discharge with eye movements in cats. Schematic diagram showing the sites stimulated and the synaptic connections identified in these experiments. A and B: intra‐ and extracellular recordings from ph neuron showing compound EPSP following stimulation of contralateral (V_c) and ipsilateral (Vi) vestibular nerves (2× threshold) in a cat anesthetized with pentobarbital. Arrows indicate synaptic latency (1.4 ms). C: neuronal activity of a burst‐tonic praepositus neuron during spontaneous horizontal eye movement in an awake cat. Lower traces indicate electro‐oculograms (OG) for horizontal and vertical eye movements in the ipsilateral eye, respectively. Arrow marks the onset of burst discharge (5 ms before EOG change). MLF, medial longitudinal fasciculus; Cer, cerebellum.

Distribution of responses evoked by stimulating a peripheral nerve in two different preparations. Top: natural stimulation of the forepaw in an unanesthetized decerebrate cat. Bottom: distribution of the responses evoked by stimulating the right sphenous nerve in a cat anesthetized with pentobarbital (Nemb.).

Summary diagram depicting the general pattern of afferent and efferent projections relating the 3 primary sagittal zones of the cerebellum to the thalamocortical system, the cerebral cortex, and the spinal cord. Notice that all cerebellar regions project to both infratentorial and supratentorial structures. X₁ through X₆ indicate different sets of neuronal interactions regulated by cerebellar output pathways. The block in the lower left represents populations of neurons in the dorsal and ventral horn activated by peripheral afferents. The regulation of these reflex pathways by cerebellar efferent systems is not depicted in this diagram.