Wide Receptive Fields Research Articles

Potential role of medullary raphe-spinal neurons in cutaneous vasoconstriction: an in vivo electrophysiological study.

In rabbits, raphe magnus/pallidus neurons form a link in the CNS pathway regulating changes in cutaneous blood flow elicited by nociceptive stimulation and activation of the central nucleus of the amygdala. To characterize relevant raphe-spinal neurons, we performed extracellular recordings from the rostral medullary raphe nuclei in anesthetized, paralyzed, mechanically ventilated rabbits. All studied neurons were antidromically activated from the dorsolateral funiculus of the spinal cord (C(8)-T(2)). Of 129 studied neurons, 40% were silent. The remaining neurons discharged spontaneously at 0.3-29 Hz. Nociceptive stimulation (lip squeeze with pliers) excited 63 (49%), inhibited 9 (7%), and did not affect 57 (44%) neurons. The same stimulation also elicited falls in ear pinna blood flow. In neurons activated by the stimulation, the increase in discharge preceded the fall in flow. Electrical stimulation of the spinal trigeminal tract excited 61/63 nociception-activated neurons [onset latencies range: 6-75 ms, mean: 28 +/- 3 (SE) ms], inhibited 9/9 nociception-inhibited neurons (onset latencies range: 9-85 ms, mean: 32 +/- 10 ms), and failed to affect 55/57 neurons insensitive to nociceptive stimulation. Neurons insensitive to nociceptive/trigeminal stimulation were also insensitive to nonnociceptive tactile stimulation and to electrical stimulation of the amygdala. They were either silent (32/45) or discharged regularly at low frequencies. They possessed long-duration action potentials (1.26 +/- 0.08 ms) and slow-conducting axons (6.0 +/- 0.5 m/s). These neurons may be serotonergic raphe-spinal cells. They do not appear to be involved in nociceptive-related cutaneous vascular control. Of the 63 neurons sensitive to nociceptive and trigeminal tract stimulation, 35 also responded to tactile stimulation (wide receptive field). These neurons possessed short action potentials (0.80 +/- 0.03 ms) and fast-conducting axons (30.3 +/- 3.1 m/s). In this subpopulation, electrical stimulation of the amygdala activated nearly all neurons tested (10/12), with a mean onset latency of 34 +/- 3 ms. The remaining 28 neurons sensitive to nociceptive and trigeminal stimulation did not respond to tactile stimuli and were mainly unaffected by amygdala stimulation. It may be that fast-conducting raphe-spinal neurons, with wide multimodal receptive fields and with input from the central nucleus of the amygdala, constitute the bulbo-spinal link in the CNS pathway regulating cutaneous blood flow in response to nociceptive and alerting stimuli.

A chronic microelectrode investigation of the tonotopic organization of human auditory cortex

We investigated the functional organization of human auditory cortex using a new chronic microelectrode technique. Tonotopic mapping data was obtained at the single unit level for the first time in humans. All sound-driven units were noted to have frequency-dependent response patterns. The majority of units (73%) demonstrated sharply tuned excitatory best-frequency responses. Twenty seven percent of units showed wide receptive fields, representing excitatory responses to almost the entire range of frequencies presented. A tonotopic pattern was observed with best frequencies systematically increasing as more medial-caudal recording sites were sampled.

Predicting the shape of distance functions in curve tracing: Evidence for a zoom lens operator

Jolicoeur, Ullman, and MacKay (1986) showed that the time to confirm that two dots are on the same curve increases monotonically, but nonlinearly, as the curve distance between the two dots increases. These displays contained two curves and two dots. On same trials, the two dots were on the same curve (target curve), while the other curve served as a foil (distractor curve). The monotonically increasing effects of curve distance on response times for same trials suggested that the intervening curve segment was traced. In the present investigation of the source of the nonlinearity in these distance functions, it was hypothesized that differences in the distractor curves may have allowed a curve tracing operator with zoom lens properties to widen its receptive field while tracing parts of certain target curves. The wider receptive field may have allowed faster tracing over certain segments, owing to a reduced number of shifts required by the operator to scan the curve. The consequence of training certain segments of the curve more quickly than other segments of the curve would be a nonlinear effect of distance. A new set of stimuli was created for testing this hypothesis directly. Fairly linear distance effects were found for stimuli that contained a distractor curve that constrained the breadth of the postulated curve tracing operator, whereas stimuli that contained a distractor curve that could allow for a larger receptive field yielded nonlinear distance functions. The results are compared with the predictions of three quantitative models: pixel-by-pixel tracing; Jolicoeur, Ullman, and MacKay's (1991) bipartite operator; and a new zoom lens model, analogous to the zoom lens model of visual attention. The results were fit best by the latter model, in which tracing is accomplished by tracking the curve with a variably sized local operator.

Spatial organization of axons in turtle visual cortex: Intralamellar and interlamellar projections

The spatial pattern of projections within turtle visual cortex was studied by using focal injections of horseradish peroxidase into visual cortex in an in vitro wholebrain preparation. Injections anterogradely filled the axons of many layer 2 neurons, which could be followed for 200-500 microns from the injection sites. Axons were typically unbranched, relatively straight, and bore small varicosities at irregular intervals. They radiated from the injection sites in all directions, but showed some preference toward orientations along the lateral-medial axis of the cortex. Earlier work (Mulligan and Ulinski, '90) had demonstrated that turtle visual cortex contains a series of isoazimuth lamellae, each representing an individual azimuth of visual space and oriented perpendicular to the rostral-caudal axis of the cortex. The present study provides evidence for intrinsic projections both along isoazimuth lamellae and between adjacent lamellae. These projections may play roles in the elaboration of wide receptive fields of cortical neurons.

The organization of receptive fields of an antero-medial group of spiking local interneurones in the locust with exteroceptive inputs from the legs

1. The receptive fields of 18 spiking local interneurones with cell bodies in an antero-medial group and unilateral arborisations in the metathoracic ganglion of the locust Schistocerca gregaria were defined by intracellular recording while mechanically stimulating exteroceptors on the middle and hind legs. 2. The receptive fields on the hind leg ipsilateral to the arborizations are divisible into 3 general categories. First are fields that consist of distinct excitatory and inhibitory regions from receptors on different parts of the leg. The boundary between these regions is set by the dorso-ventral axis of the leg. Second are fields that are entirely excitatory and third are fields that are entirely inhibitory. These fields may cover the entire surface of the hind leg. 3. Sixteen of the interneurones also have receptive fields on the ipsilateral middle leg. These fields are either wholly excitatory or wholly inhibitory and may correspond in position to the field on the ipsilateral hind leg. Furthermore, many interneurones are also excited or inhibited by inputs from the contralateral middle or hind legs. 4. These interneurones integrate the mechanosensory signals from a hind leg in parallel with midline spiking local interneurones and should therefore play a role in the expression of local reflexes. Their wider receptive fields, however, suggests that they also influence the coordination between the legs in posture and locomotion.

Interactions of visual stimuli in the receptive fields of inferior temporal neurons in awake macaques.

Monkeys were trained to perform a fixation task and a visual discrimination task. During the fixation task, one or two light bars were presented at different positions in the receptive fields of TE neurons. During the discrimination task, the animal was required to detect the positive stimulus when one or two of the paired small colored spots or two-dimensional patterns were presented. In both behavioral conditions, when the two light stimuli were presented simultaneously, almost none of the TE neurons showed an increase in responding over the single stimulus condition; the response was usually similar or less than the stronger response in the single stimulus condition. In the neurons that responded selectively to the discriminanda during the discrimination task, various interactions between the two antagonistic stimuli occurred depending on the location or the effectiveness of the two stimuli. These results may be related to gain control mechanisms in the wide receptive fields of TE neurons.

Retinal constraints on orientation specificity in cat visual cortex

Most retinal ganglion cells (Levick and Thibos, 1982) and cortical cells (Leventhal, 1983; Leventhal et al., 1984) subserving peripheral vision respond best to stimuli that are oriented radially, i.e., like the spokes of a wheel with the area centralis at the hub. We have extended this work by comparing directly the distributions of orientations represented in topographically corresponding regions of retina and visual cortex. Both central and peripheral regions were studied. The relations between the orientations of neighboring ganglion cells and the manner in which the overrepresentation of radial orientations is accommodated in the functional architecture of visual cortex were also studied. Our results are based on an analysis of the orientations of the dendritic fields of 1296 ganglion cells throughout the retina and the preferred orientations of 1389 cells located in retinotopically corresponding regions of cortical areas 17, 18, and 19 in the cat. We find that horizontal and vertical orientations are overrepresented in regions of both retina and visual cortex subserving the central 5 degrees of vision. The distributions of the orientations of retinal ganglion cells and cortical cells subserving the horizontal, vertical, and diagonal meridians outside the area centralis differ significantly. The distribution of the preferred orientations of the S (simple) cells in areas 17, 18 and 19 subserving a given part of the retina corresponds to the distribution of the dendritic field orientations of the ganglion cells in that part of retina. The distribution of the preferred orientations of C (complex) cells with narrow receptive fields in area 17 but not C cells with wide receptive fields in areas 17, 18, or 19 subserving a given part of the retina matches the distribution of the orientations of the ganglion cells in that part of retina. The orientations of all of the alpha-cells in 5-9 mm2 patches of retina along the horizontal, vertical, and oblique meridians were determined. A comparison of the orientations of neighboring cells indicates that other than a mutual tendency to be oriented radially, ganglion cells with similar orientations are not clustered in the retina. Reconstructions of electrode penetrations into regions of visual cortex representing peripheral retina indicate that columns subserving radial orientations are wider than those subserving nonradial orientations. Our results provide evidence that the distribution of the preferred orientations of simple cells in visual cortex subserving any region of the visual field matches the distribution of the orientations of the ganglion cells subserving the same region of the visual field.(ABSTRACT TRUNCATED AT 400 WORDS)

Nonspiking local interneurons mediate surround inhibition of crayfish sustaining fibers

1. A class of local, non-spiking interneurons in the second optic lobe of the crayfish is described, and their role in mediation of surround inhibition of sustaining fibers (SFs) is examined. 2. Surround inhibition in SFs is not associated with a measurable IPSP or postsynaptic conductance change in SFs and thus is produced by a decrease in the level of exciatory synaptic input (Fig. 1). 3. Local (amacrine) interneurons in the medulla, the second optic lobe, have biplanar dendritic trees. The proximal plane is coextensive with the single plane of SF dendrites (Fig. 2). 4. The amacrine cells respond to light with a graded depolarization but without impulses (Figs. 3 and 4). Depolarization with extrinsic current strongly reduces ongoing light-induced SF firing, and hyperpolarization enhances SF firing (Fig. 7). 5. Amacrine cell light responses share many properties with SF surround inhibition, including wide receptive fields (Fig. 4), response waveform and time course, and tonic light responses which are proportional to the log of the light intensity (Fig. 5). 6. When sinusoidal current is injected into an amacrine cell (Fig. 9) the SFs exhibit a peak sensitivity to current at modulation frequencies of 2–4 Hz and a flat response above about 10 Hz. SFs exhibit a similar frequency sensitivity to the modulation of illumination in the inhibitory surround. 7. Several results imply that the amacrine cells provide feedback or recurrent inhibition to the excitatory visual pathway.

Near-field acuity after visual system lesions in pigeons. I. Thalamus

Visual acuity determinations were made for 14 pigeons trained to discriminate high-contrast, square-wave gratings of successively higher spatial frequencies from blank stimuli of equal average luminances. The stimuli were presented according to the method of constant stimuli. Video-taped motion pictures of the key-pecking response provided a measure of the cornea-to-stimulus distance. The preoperative results indicated that the mean minimal-separable visual angle was 2.3 min (range 1.6–3.6) under conditions of photopic adaptation with the stimulus luminance at 70 cd/m 2. When performance was stable, bilateral electrolytic lesions were placed in: (1) nucleus rotundus (RT), (2) nucleus opticus principalis thalami (the OPT complex); and (3) RT plus the OPT complex. Lesions confined to the OPT complex did not impair resolution threshold while lesions confined to the nucleus rotundus produced permanent threshold elevations. When the destruction of OPT and RT was combined, the deficit was more severe. The results indicated that the integrity of the tectofugal pathway of the pigeon is required for normal performance of spatial frequency discrimination near threshold. These observations suggest that nuclei containing neurons with wide receptive fields are capable of processing visual information with fine spatial detail.

The morphological diversity and receptive fields of spiking local interneurons in the locust metathoracic ganglion

Twenty-one types of spiking local interneurons are described in a segmental ganglion of the locust. All have their cell bodies in a group at the ventral midline of the metathoracic ganglion. The interneurons are characterized by their shape as revealed by intracellular injection of dye, and by their physiology as revealed by intracellular recording. Each interneuron conforms to a basic plan, but the characteristic shape of each is derived from the elaboration of branches in some regions of the neuropil and by their absence in other regions. Some interneurons have ventral branches that extend over most of one-half of the metathoracic neuropil, whilst others have ventral branches restricted to a small region of neuropil. A few interneurons have dorsal branches that enter the first abdominal neuromere . Each type of interneuron is excited by a specific array of mechanoreceptors on the hind leg ipsilateral to its neuropilar branches. Some interneurons have a wide receptive field that encompasses most of the dorsal surfaces of the distal three parts of a leg, whilst others have a field limited to the spurs at the distal end of the tibia. The relationship between the shape of an interneuron and the size or orientation of its receptive field is discussed.

Responses of cat auditory cortical neurons to tones of different frequencies and electrical stimulation of corresponding regions of the cochlea

Characteristic frequencies of neurons in the cat auditory cortex (area AI) whose receptive fields are located in different parts of the basilar membrane of the cochlea were determined in cats anesthetized with pentobarbital. The higher the characteristic frequency of a neuron in area AI, the nearer its receptive field lies to the base of the cochlea. Receptive fields of neurons with a characteristic frequency higher than 4 kHz lie on the first 10 mm of the basilar membrane. Receptive fields of neurons with a characteristic frequency below 4 kHz lie on the remaining 11–12 mm of the membrane. The effect of electrical stimulation of the center of the receptive field of a neuron corresponds to its response to a tone of characteristic frequency. The more the frequency of the acting tone differs from the characteristic frequency, or the further the point of stimulation from the center of the receptive field of the neuron, the less likely is the neuron to respond with an action potential. Neurons with a low characteristic frequency have wider receptive fields than neurons with a high characteristic frequency. Receptive fields of neurons with close characteristic frequencies on the basilar membrane overlap considerably. It was shown by the method of paired stimulation that excitation evoked in neurons in area AI by the action of a tone of a particular frequency is followed by long-lasting inhibition. This inhibition lasts longest and is most effective if a tone of the characteristic frequency is used.

Visual responses of nucleus corticalis neurons in the perciform teleost, Northern Rock Bass ( Ambloplites rupestris rupestris)

Intracellular recordings were made from neurons in the nucleus corticalis (NC), a large-celled nucleus situated along the medial edge of the tectum in teleost fish. The NC cells had wide receptive fields and responded to small moving spots contrasting with the background. They were non-directional, habituated quickly, and some were bimodal.

Receptive field of the stemmata in the swallowtail butterflyPapilio

Receptive fields of individual retinular cells in the stemmata ofPapilio xuthus L. were examined electrophysiologically, and the receptive field of the complete stemmatal system was reconstructed (Fig. 8). In stemmata I-IV, proximal retinular cells have narrow receptive fields (acceptance angles of Δϱ = 1.7–5 °, Fig. 5) and small inclinations of the visual axes (inclinations of θ = 0.7–1.5 °, Fig. 2) with respect to the axis of the stemma, while distal ones have wide fields (Δϱ =7–13 °, Fig. 5) and large inclinations of the visual axes (θ = 5–10 °, Fig. 3). In stemmata V and VI, both proximal and distal retinular cells have wide receptive fields (Δϱ = 7–26 °, Fig. 6) and have large inclinations of their visual axes (Δ = 9–19 °) with respect to the axis of the stemma except for one proximal cell (θ = 0 °) (Fig. 4). The spatial properties of distal and proximal retinular cells, combined with the finding that distal cells are homogeneous in the spectral sensitivity while proximal ones are heterogeneous (Ichikawa and Tateda 1980), suggest that the distal cells may be concerned largely with the detection of objects and proximal cells are involved with the discrimination of the color and shape of the detected objects.

Receptive field patterns in photoreceptors of the fly

1. The shape of the receptive field in the photoreceptors of the flesh fly,Boettcherisca peregrina, compound eye was contoured by using the intracellular responses to illumination from different positions around the compound eye. 2. The shapes of these contours were classified into six patterns. Type A was roughly round and small, corresponding to the normal receptive field. Type B was similar to type A in shape but was larger. Type C was large and stellate in shape with spokes radiating along thex, y andz axes of the alignment of the onimatidia. This type was classified into three sub-groups: type C1 with spokes along all of thex, y andz axes; type C2 with spokes along thex andy axes; and type C3 with spokes along thex andy axes except in an upward direction. Types D, E and F were very long and extended in one direction. The direction of extension was horizontal, oblique and vertical in types D, E and F, respectively. Type E was classified into two sub-groups, E1 and E2, based on the direction of the oblique extension. One or more areas with high sensitivity (subpeaks) at the tip of the extending field in these large fields were found. 3. Type A was most frequent, followed by type B. Types D, E and F were more common than type C. 4. In contrast to the spectral sensitivity determined by axial illumination, the second peaks of the blue range were found to be diminished when measured by non-axial illumination, even if their positions were in the peripheral area or the sub-peaks. 5. The size of the acceptance angle was smaller in types A and C than in the other types. The angle in type A was smallest at the antero-medial region of the compound eye and became larger with increasing distance laterally from the antero-medial region. 6. The different receptive field types were not evenly distributed throughout the eye. The cells of types A and B were found mainly in the antero-medial region but were scattered over the compound eye. The cells of type C were limited to a small area in the antero-medial region.The cells of types D, E and F were distributed throughout the lateral region of the compound eye. 7. The receptive fields in light- and dark-adapted eyes showed no difference in their patterns, although the acceptance angle of each peak within the receptive field became slightly narrow under light-adaptation. This result may suggest that migration of the screening pigment is negligible. 8. No facilitatory or inhibitory interactions appeared between the responses elicited by illuminations from two different positions within the wide receptive field. The responses were summative. 9. Latencies of the responses were the same under axial or non-axial illumination in type A cells with the usual, small receptive field. In contrast, the responses of cells with wide receptive fields showed step-like prolongation of the latency with increasing distance of the illuminating position from on-axis. The phase of the polarization sensitivitiy curves shifted when the receptive field measured under illumination from each position corresponding to the occurrence of the step-like prolongation of the latency indicating that the wide receptive field is composed of inputs from different photoreceptors. 10. The present study suggests that the origin of the wide receptive field in the photoreceptor is neuronal.

Response properties of units in the lateral geniculate nucleus of the domestic chick ( Gallus domesticus)

One hundred and four visual units of the (ventral) lateral geniculate nucleus (GL) of chicks (Gallus domesticus) were studied with extracellular microelectrodes. Most were extremely responsive to moving targets even at low speeds (0.1 degrees/sec). They were classified as follows. (1) movement-sensitive units with uniform, restricted receptive fields (47%). (2) Movement-sensitive units with small receptive fields possessing regions responding to differing modes of stimulation ('center-periphery units'). (3) Movement-sensitive neurons with uniform, wide receptive fields, larger than 75 degrees x 65 degrees (15%). (4) Movement-insensitive cells, responsive only to illumination changes (7%). (5) Units with indeterminate receptive fields, a poor visual response or a poor response to movement (14%). The firing of neurons in classes I-III was mostly an accurate function of target speed; half of them also provided accurate monitoring of the beginning, course and termination of target movement (tonic units). In view of the above, the high proportion of directionally selective cells (31%) and the large size of many of its receptive fields, the GL is considered as a candidate structure for optomotor integration but the evidence is otherwise scant. There is, however, an apparent contribution to its unit properties from both retinal ganglion cells and neurons from different tectal layers. Whatever its role, it is unlikely to be the functional homologue to the mammalian ventral lateral geniculate as the unit properties of two structures differ substantially.

Diencephalic binocular wide field neurons in the frog

Single binocular neurons were recorded in the frog diencephalon (area dorsalis posterior and area ventralis thalami). These neurons respond to any moving stimulus from 1 degree 30 to 32 degrees in diameter, without directional selectivity and to an ON-OFF light stimulation. They are not activated by stationary objects. Habituation is also commonly observed. The most important feature of these neurons is their wide receptive field which covers the whole visual field of the frog. Evidence that these neurons receive inputs from each tectum is discussed.

Neuronal analysis of skin sensitivity representation in the red nucleus of the alert cat

Responses of the cat's red nucleus to skin stimulation were studied in a chronic experiment by means of the microelectrode technique. The majority of red nucleus neurons had wide receptive fields in which there were areas causing the most intensive and stable activation of the corresponding neurons. A somatotopic principle of skin sensitivity representation in the red nucleus is revealed. After destruction of the cerebellar nuclei and sensorimotor cortex the background activity of red nucleus neurons was reduced, the responses to skin stimulation changed, the peripheral receptive fields got narrower and rearranged. Even so the somatotopic character of skin sensitivity representation in the red nucleus was preserved.

The ventral spino-olivocerebellar system in the cat III. Functional characteristics of the five paths

1. Five spino-olivocerebellar paths ascending through the ventral funiculus (VF-SOCPs) with different projection zones in the cerebellar cortex have been distinguished (Oscarsson and Sjöuld, 1977). The paths are denoted the a-, b1-, b2-, c1- and c3-VF-SOCPs according to the labelling of the projection zones. The functional organization of these paths has now been investigated. 2. All five paths are activated by the flexor reflex afferents from wide receptive fields (one or more limbs). Distal nerves are more effective in evoking responses than proximal nerves. 3. The a-, c1- and c3-paths are activated from the ipsilateral hindlimb only. The b1- and b2-paths are activated bilaterally from the forelimbs and hindlimbs, respectively. 4. The a-, b1- and b2-paths have long segmental delays indicating a polysynaptic linkage between the primary afferents and the tract neurones, whereas the c1- and c3-paths have short delays demonstrating a monosynaptic linkage. 5. The neurones giving origin to the paths are situated within a few segments of the dorsal root entrance. The axons cross the midline, ascend through the contralateral ventral funiculus, and activate the olivary neurones monosynaptically. 6. The spino-olivary tract of the c3-path has an upper conduction velocity of 30 m/s, whereas the other paths have upper conduction velocities of 40--45 m/s. 7. The segmental delay of the b1-VF-SOCP is much longer (mean 8.7 ms) than that of the b2-VF-SOCP (mean 3.9 ms). As a result simultaneous stimuli to the hindlimbs and forelimbs are signalled to reach the cerebellar cortex at the same time. 8. It is suggested that the information carried by the different paths is concerned with the segmental motor control.

Some spatial properties in the first optic ganglion of the fly

Spatial properties in the first optic ganglion ofCalliphora stygia were studied electrophysiologically. 1. In the lamina cells, previously described as type I, L1–2 or large unipolar cells, inhibitory processes were demonstrated around the centres of the receptive fields by stimulating with two short slits separated by different distances or one slit with different lengths. Although inhibitory effects were demonstrated by stimulating around the centre of the receptive field, where the largest hyperpolarizing potential was produced, inhibitory effects were not necessarily seen at equal distances in all directions from the centre, but appeared at different distances in different directions. The distances of the inhibitory area from the centre of the receptive field were in the range of 2° to 3.5° in the visual angle. And some directional selectivity in the response was seen, with respect to the orientation of the slit stimuli. 2. A different class of lamina cell (called wide field lamina cell here) with very wide receptive fields (up to 50° or even 70°) could also be recorded intracellularly. The waveform and intensity function of the hyperpolarizing responses elicited in these cells were similar to those of the usually recorded lamina cells mentioned above. Inhibitory phenomena as described above were also demonstrated in cells of this type. The receptive field of this cell type is complex, apparently being primarily excited along three intersecting axes which can be seen to contribute to the directional selectivity of the cell's graded responses to differently oriented slits. In addition, in one cell, depolarizing responses were observed in a pair of restricted areas contained in the opposite angles of two of the intersecting axes. Inhibitory interaction between hyper- and depolarizing responses was demonstrated by simultaneous illumination of both regions.

Reticulospinal neurons with and without monosynaptic inputs from cerebellar nuclei.

An account is given of the responses of 557 medial reticular neurons with axons projecting down the spinal cord. All 30 experiments were on decerebrated unanesthetized cats paralyzed by Flaxedil. Recording from single neurons was by extracellular glass microelectrodes. Identification was first by location (confirmed by subsequent histology) in the medial reticular nucleus of medulla or pons, and second by antidromic activation from cord stimulation at C2 and L2 segmental levels. Axonal conduction velocities were calculated from the latency differential between L2 and C2 antidromic responses, and were usually in the range of 90-140 m/s; but about 25% were slower, ranging down to 30 m/s. Stimulation by electrodes in the ipsilateral and contralateral fastigial nuclei differentiated reticulospinal neurons into two classes according to whether they did or did not receive monosynaptic inputs, the respective populations of fully investigated neurons being 270 and 174. The fastigioreticular neurons were distinguished by a higher background frequency with mean values of 28 as against 15/s. There were also significant diffences in both the excitatory and inhibitory responses to afferent volleys from forelimb and hindlimb nerves. Comparison of the respective latency histograms showed that the responses of neurons with a fastigial input had an excess of latencies in the ranges that can be correlated with the latency histograms observed for fastigial responses. Thus, there is evidence for the effectiveness of the fastigial input and so for the pathway with monosynaptic linkage: Purkinje cells of cerebellar vermis yields fastigial neurons yields medial reticular neurons projecting down the spinal cord. Adequate stimulation of cutaneous receptors by pad taps and air-jet stimulation of hairy skin in a disppointingly small action when compared with fastigical responses. Explanations of this deficiency are suggested. Another discrpancy from the fastigial responses is that the medial reticular neurons have much wider receptive fields with little discrimination between ipsilateral and contralateral and between forelimb and hindlimb. Stimulation of the ipsilateral tegmental tract was tested on 183 reticulospinal neurons, 112 being with fastigial inputs. In about half there was a powerful monosynaptic excitation, which would identify such neurons as being on the pathway from mesencephalic and diencephalic centers to the spinal cord. There is a general discussion of transmission across successive synaptic relays, where specificity is sacrificed to integration.