The perineuronal net in the fastigial nucleus of the rat cerebellum

Brain Structure and Function - The morphological study of the rat fastigial nucleus with the Golgi-Rio Hortega method showed the presence of glial perineuronal nets surrounding the large neurons,...     

Attenuation of septal hyperemotionality by cerebellar fastigial lesions in the rat

Lesions of the cerebellar fastigial nucleus were found to greatly attenuate the hyperemotionality produced by simultaneous septal lesions in the rat. Lesions dorsal or lateral to the fastigial nucleus had no effect. This lesion-related attenuation of emotionality produced by fastigial destruction appeared quite specific. Other motivated behaviors such as food intake and activity were not affected. Further, the characteristic increase in social contacts seen after septal destruction was not altered by the fastigial lesions. The results support the view that the cerebellar fastigial nucleus is part of a complex limbic-brainstem network involved in the control of emotional and motivational behaviors.     

A Golgi study of the lateral reticular nucleus in the rat

Summary The organization of the lateral reticular nucleus (LRN) of the rat was investigated by using the Golgi technique. Golgi-Cox preparations revealed neurons with shapes similar to those observed in Nissl-stained preparations. Fusiform cells possess rectilinear dendrites with secondary dendrites which are longer than the parent stem. The remaining cell types have short dendrites which branch for three or four generations and follow a tortuous course. These two types of neurons are similar to the isodendritic and allodendritic neurons which have been reported in the reticular formation. The neurons throughout the LRN form cell clusters. In Golgi preparations five to ten cells are seen in each cluster but counterstaining reveals that the clusters are made up of many more cells than the Golgi preparations suggest. Many cells lie in close apposition and the dendrites of the cells in each cluster intertwine to form dendritic plexuses. Dendritic input from both neighbouring and distant cell clusters also contributes to the plexus formations within each cell cluster. Under high magnification, the dendrites show irregularities in their contours, including warty excrescenses, bumps and an array of spines, some of which are pedunculated. The appendages are confined primarily to distal portions of the dendrites, with few spines observed on the somata and proximal dendrites. Varicosed dendrites are also in common occurrence throughout the nucleus.     

The pathways responsible for excitation and inhibition of fastigial neurones

Summary A detailed study of the latencies of the excitatory responses of fastigial cells disclosed an unexpected anomaly. Except for infrequent small responses the latency was many milliseconds longer than would be expected for excitation by axon collaterals of the fast spino-cerebellar pathways. There were many examples in which inhibition had an earlier onset than excitation; nevertheless the inhibitory latency was not so brief as to preclude its production by Purkyn cell discharge in response to the fast spino-cerebellar pathways. Histograms have been constructed for the latencies of the excitation and inhibition evoked in fastigial cells by four kinds of inputs: nerve volleys from forelimb and hindlimb; pad taps from forelimb and hindlimb.Electrical stimulation of the lateral reticular nucleus on the same side very effectively excited fastigial cells, usually with the latency expected for monosynaptic excitation. It was therefore postulated that with forelimb and hindlimb stimulation the dominant mode of excitation of fastigial cells was by excitatory collaterals from the spino-reticulo-cerebellar pathway. Stimulation of the contralateral inferior olive also was effective in evoking a short latency excitation of fastigial cells. It was therefore assumed that collaterals from the spino-olivo-cerebellar pathway provide an additional excitatory input to fastigial cells.A diagram was constructed in space-time coordinates graphically expressing the timing of the various excitatory and inhibitory pathways by which a hindlimb nerve stimulus acts on fastigial cells. An interesting design feature is thereby disclosed, namely that the dominant excitatory input to the fastigial cells via the slower spino-cerebellar paths is virtually synchronous with the inhibitory input from Purkyn cells discharging in response to the fast spino-cerebellar input. It is pointed out that the temporal pattern gives optimal conditions for the computer-like operation of the fastigial nucleus.     

Neurogenesis in the cerebellum of the rat: An autoradiographic study

Summary Time of origin of various neuronal elements in the cerebellum of rat was established with the aid of tritiated-thymidine-autoradiography. The earliest nerve cells to form were the Purkinje cells, and they came into existence on days 15 and 16 of gestation. Interstitial nerve cells had their genesis on days 15, 16, 17 and 18, and the marginal cells on day 16 of the embryonic development. The Golgi cells were found to come into existence on days 17, 18 and 19 of gestation. On day 21 of gestation a number of small-medium-sized nerve cells, which were smaller than the Golgi cells but larger than the granule cells, were seen to come into existence. Finally, the earliest stock of granule, basket and stellate cells, primarily in the nodulus, flocculus and para-flocculus, were observed to have been formed on the day 21 of embryogenesis.This research was supported by NIH Research Grant No. NS-08817-03. Histological work by Sheila Anderson and photographic work by Donna Whitehurst is gratefully acknowledged.     

A schematic atlas of the cerebellum of the rat

Thirty-two sagittal and 22 frontal sections of the albino rat cerebellum are shown. The illustrations are based on stained sections which were redrawn with help of a microprojector. The selection of sections emphasizes areas of the cerebellum which contain the cerebellar nuclei. Each section is provided with stereotaxic coordinates.     

Multiple representation in the nucleus lateralis of the cerebellum

Summary The motor organization of the nucleus lateralis (NL) of the rat's cerebellum was investigated by observing the motor effects of electrical microstimulations of the NL. The movements evoked by the NL mainly concerned forelimb and head segments. Only in a few cases were movements of hindlimb segments evoked. Motor effects were obtained according to a precise topographical pattern. This pattern delimited functional zones, or representations, within the NL, each zone being specifically related to a particular segment of the body. A few body segments were activated from single zones only (single representation) whereas some other body segments could be activated from different zones of the NL. Among them, the axio-proximal body segments were activated in a similar way from all sites (multiple representation) whereas the distal body segments were differently activated from the various representation zones (specific representation). The multiple and specific representations were distributed between the 3 cytoarchitectonic subregions of the NL (NLm, DLH and slp) in such a way that the body segments were usually represented only once in each individual NL subregion. Each NL subregion included sets of representations concerning body segments characterized by a topographical continuity (e.g. the different segments of the forelimb in both DLH and slp). Thus, the individual NL subregions may bring into play coordinate plurisegmental muscular activities of the limbs and/or of the head. The NLm controls movements of all the segments of the head and those of axio-proximal segments of both limbs. The DLH particularly controls movements of the head, including both the proximal (neck) and the oral regions. To a lesser degree, DLH controls movements of the various segments of the forelimb, including synchronous flexion of all the digits. The slp is specifically involved in the control of motor activities of: i) the proximal segment of the head (rotation of the neck) as well as its distal segments (displacement of individual vibrissae, rotation of the ear pinna) and ii) the various segments of the forelimb including individual digits. Functionally, the proximal segments would be concerned in the spatial displacement of the limbs or of the head whereas the distal segments would be involved in the realization of precise and discrete movements related to specific functions of the distal segments concerned. The 3 subregions of the NL may be concerned in different motor functions. The results suggest the involvement of: i) the NLm in the postural adjustments of the body, or of part of it; ii) the DLH in motor behaviours which integrate the oral and the forelimb motor activities; iii) the slp in exploratory activities (by moving individual vibrissae, the ear pinna and individual digits) and/or in discrete manipulative activities.     

An investigation of a possible direct projection from the medial nucleus of the cerebellum to the paraventricular nucleus of the hypothalamus in the rat: a study using retrograde WGA-HRP and Fluoro-Gold tracing techniques

Retrograde transport of lectin-conjugated horseradish peroxidase and Fluoro-Gold was used in an attempt to obtain data to confirm the existence, predicted from physiological studies, of a direct, monosynaptic projection from the medial nucleus of the cerebellum (MN) to the paraventricular nucleus of the hypothalamus (PVH) in the rat. Injections of these two tracers that included the PVH and surrounding diencephalic structures, or that in the case of Fluoro-Gold were localized to the PVH, resulted in retrograde neuronal labeling in widely separated nuclei known to project to the areas included in the injection sites. Thus, effective uptake and transport of both tracers occurred under the experimental conditions employed in this study. However, injections confined to the PVH and regions of the hypothalamus adjacent to it, or to the PVH alone, produced no retrograde neuronal labeling in the medial nucleus, indicating that the MN does not project directly to the PVH. Alternative explanations for the findings from physiological experiments were sought. The possibility that electrical stimulation of fibers of passage through the region of the MN might produce a monosynaptic response in the contralateral PVH was discarded, because retrogradely labeled neurons in nuclei such as the locus ceruleus and lateral parabrachial nucleus were distributed mainly ipsilateral to hypothalamic injection sites. However, tracer injections into the MN produced retrograde labeling of neurons in the same region of the lateral paragigantocellular nucleus (LPGi) in which labeled cells were found following tracer injections into the PVH. Axon collaterals of individual neurons in the LPGi might, therefore, project both to the MN and to the PVH. The possibility that such a circuit could, in the absence of a direct MN to PVH projection, provide the basis to explain the physiological findings is discussed.Abbreviations CVL Caudal ventrolateral medulla - DAO dorsal accessory olive - F fornix - FDP fastigial depressor response - FG Fluoro-Gold - FPR fastigial pressor response - LC locus ceruleus - LHA lateral hypothalamic area - LPB lateral parabrachial nucleus - LPGi lateral paragigantocellular nucleus - LRN lateral reticular nucleus - MAO medial accessory olive - MN medial nucleus of the cerebellum - NTS nucleus of the tractus solitarius - PVH paraventricular nucleus of the hypothalamus - RVL rostral ventrolateral medulla - SCP superior cerebellar peduncle - SFO subfornical organ - V ₃ third ventricle - V ₄ fourth ventricle - WGA-HRP wheat germ agglutinin-conjugated horseradish peroxidase     

Cerebellar stimulation modulates the intensity of a visceral nociceptive reflex in the rat

The cerebellum modulates different nociceptive phenomena and influences visceral functions. This study shows cerebellar modulation of an abdominal reflex elicited by a visceral noxious stimulus (colorectal distension, CRD). The intensity of the reflex was measured by electromyographic (EMG) recording from the rectus abdominus muscle, and the cerebellar cortex (vermis, lobule VIII), the fastigial nucleus, or the dentate nucleus was stimulated using D, L-homocysteic acid (0.1 M, 1 micro l). To release the fastigial nucleus from inhibition by the Purkinje cells, bicuculline (GABA(A) receptor antagonist, 100 micro M, 1 micro l) was used. Stimulation of the cerebellar cortex enhanced, whereas stimulation or disinhibition of the fastigial nucleus decreased, the responses to CRD measured by EMG. Stimulation of the dentate nucleus did not have an obvious effect on the intensity of the reflex. These results are in agreement with the hypothesis that the cerebellum modulates visceral nociceptive functions, whereby the cerebellar cortex and the fastigial nucleus, respectively, play a pro-nociceptive and an anti-nociceptive role.     

An ultrastructural study of the lateral reticular nucleus in the rat

Summary A systematic study of the normal synaptic patterns within the lateral reticular nucleus (LRN) of the rat revealed various synaptic relationships. Two types of axon terminals were identified according to the morphology of the synaptic vesicles contained within them. Axon terminals with round vesicles established asymmetrical synaptic contacts with the somata and all areas of the dendritic trees including somatic and dendritic appendages. Pleomorphic-vesicle terminals established symmetrical synaptic contacts on somata and their appendages and on all sizes of dendrites and their appendages. Both round and pleomorphicvesicle terminals were infrequently seen to synapse upon the somata and proximal dendrites. The round-vesicle terminals outnumbered the pleomorphic-vesicle terminals on the dendritic trees. Terminals of the en passant type were also common throughout the LRN. Both round and pleomorphic-vesicle terminals were observed simultaneously contacting the soma and one or more dendritic profiles, or two different dendritic profiles. Synaptic configurations (glomeruli) were also observed in all three divisions of the nucleus. They consisted of a large, central, round-vesicle terminal contacting a number of small-calibre dendritic processes. This arrangement was surrounded by one or more sheets of glial lamellae. Puncta adherentia were observed on the apposed membranes of adjacent cells, adjacent dendrites and adjacent axon terminals.     

Somatotopical organization of the projection from the nucleus interpositus anterior of the cerebellum to the red nucleus. An experimental study in the cat with silver impregnation methods

Summary Small lesions were done in various areas of the nucleus interpositus anterior (NIA) of the cerebellum, and the distribution of terminal degeneration was studied in the red nucleus with the methods of Nauta and Glees. The NIA projects to the contralateral red nucleus. Two principles of organization can be demonstrated in the projection: a caudorostral arrangement in the red nucleus corresponds to a mediolateral organization in the NIA and a mediolateral arrangement in the red nucleus corresponds to a caudorostral organization of the NIA. The latter distribution coincides with the somatotopical areas of the red nucleus defined by Pompeiano and Brodal (1957). Special attention has been paid to the questions of the subdivision of the cerebellar nuclei and of the course of the fibres issuing from the nuclei in the cerebellar hilus. The present findings on the projection of the NIA to the red nucleus have been correlated with recent anatomical and physiological data on the cerebellum and the red nucleus.Abbreviations BC brachium conjunctivum - c caudal - d dorsal - Ext extensor effects - Flex flexor effects - forel forelimb area - HB hook-bundle - Hb. P habenulo-peduncular tract - hindl hindlimb area - I lateral - m medial - NF nucleus fastigii or medialis - NIA nucleus interpositus anterior - NIP nucleus interpositus posterior - NL nucleus lateralis - r rostral - v ventral - III root fibres of the third nerve - IV fourth ventricle Fellow of the Canadian Medical Research Council.     

Divergent axon collaterals to cerebellum and amygdala from neurons in the parabrachial nucleus, the nucleus locus coeruleus and some adjacent nuclei

Summary After injections in the cat of Rhodamine labelled latex microspheres in the amygdala and of Fast Blue in the cerebellum neurons labelled with one of these tracers as well as some double labelled neurons were found in the parabrachial nucleus, the nucleus locus coeruleus and some adjacent nuclei (the nucleus subcoeruleus and the pontine tegmental reticular formation). All double labelled cells were located on the ipsilateral side. A few double labelled neurons were also found bilaterally in the dorsal raphe nucleus. It therefore appears that a certain number of cerebellar projecting neurons in these brain stem nuclei by means of divergent axon collaterals also project to the amygdala. The location of the double labelled cells found in this study suggests that at least some of the neurons are catecholaminergic. The findings are related to previous reports on the distribution of catecholaminergic neurons and on the amygdaloid and cerebellar projections from this part of the brain stem, and the possible involvement of these connections in cerebellar non-somatic responses are discussed. Some comments are made concerning the use of fluorescent latex microspheres for double labelling studies in combination with another fluorescent tracer.     

A horseradish peroxidase study of the projections from the lateral reticular nucleus to the cerebellum in the rat

Summary The projection from the lateral reticular nucleus (LRN) to the cerebellar cortex was studied in the rat by utilizing the retrograde transport of horseradish peroxidase (HRP). In order to study the topographic features of this projection, small amounts of HRP were injected into various sites in the cerebellar cortex. The results demonstrated that the caudal lobules of the anterior lobe vermis tend to receive afferents from the medial LRN and the rostral lobules of the vermis receive afferents from more laterally situated cells. Lobules IV and V receive inputs primarily from the magnocellular division of the LRN of both the ventromedial and dorsolateral parts of the LRN, while lobules II and III receive inputs mainly from cells which lie in the border area between the parvocellular and magnocellular division of the ventromedial part. Following injections within various areas of the posterior lobe vermis, the results indicated that lobule VIII receives the most abundant projection from the LRN and that the cells of origin are present within the parvocellular and the adjacent part of the magnocellular division throughout the rostrocaudal extent of the LRN. Following injections within lobules VI and VII, few labelled cells were found and they tended to lie within the rostral two-thirds of the magnocellular division. Little or no projection from the LRN to lobule IX was evident. The hemispheres were found to receive a modest projection from the dorsal aspect of the LRN. The projection to lobulus simplex originates mainly from the caudal two-thirds of the magnocellular division, while the projection to the ansiform and paramedian lobules originates mainly from the dorsal aspect of the rostral two-thirds of the magnocellular division. Finally, there appears to be extensive overlapping of the orgins of all three projections to the cerebellar cortex studied, and this occurs within the central area of the magnocellular division throughout the rostrocaudal extent of the LRN.     

The central cervical nucleus in the cat. III

Summary Injections of ³H-leucine were made into the region of the central cervical nucleus (CCN) in the C1–C4 segments of the spinal cord in 19 adult cats. In the cerebellum labelled mossy fibre terminals were found bilaterally concentrated in lobule I and adjoining parts of lobule II of the anterior lobe. In addition, a fair number of terminals were found in the basal parts of lobules III–VIII. The terminals were mainly found in the vermal zone. Only a minor proportion was observed in the intermediate zone of the anterior lobe and only occasionally were terminals seen in the hemispheral parts. No labelled climbing fibres were observed. Axons probably derived from the CCN were found to ascend in the brain stem, mostly contralateral to the injection site. They passed close to the vestibular nuclear complex and some fibres appeared to terminate in the nucleus x of Brodal and Pompeiano. The majority of axons entered the cerebellum via the superior cerebellar peduncle, a few via the restiform body. The findings suggest that lobules I–II are important recipients of information from the neck.Abbreviations b.c. brachium conjunctivum - c. r. restiform body - DV descending (inferior) vestibular nucleus - fl. flocculus - 1. pmd. ant. pars anterior of paramedian lobule - 1. pmd, copul. pars copularis of paramedian lobule - 1. pmd. post. pars posterior of paramedian lobule - LRN lateral reticular nucleus - LV lateral vestibular nucleus - MV medial vestibular nucleus - N.d. dentate (lateral) nucleus - N.f. fastigial (medial) nucleus - N.i. nucleus interpositus - N. mes. V mesencephalic nucleus and tract of the trigeminal nerve - N.p. pontine nuclei - N.pr. V principal nucleus of the trigeminal nerve - N. V motor trigeminal nucleus - n. VII facial nerve - N. XII hypoglossal nucleus - 01. i. inferior olive - 01. s. superior olive - pfl. d. dorsal paraflocculus - pfl. v. ventral paraflocculus - SV superior vestibular nucleus - Tr. V spinal tract of the trigeminal nerve - x nucleus x of Brodal and Pompeiano (1957) - I-X cerebellar lobules I-X according to Larsell (1953)     

Spinal projections to the lateral reticular nucleus in the rat

Summary The synaptic relationships and the distribution of the afferent terminals of the spinal pathway to the lateral reticular nucleus (LRN) of the rat were examined following induced degeneration. After high cervical hemisections, the spino-LRN projection was first examined with the Fink-Heimer silver impregnation method. Degeneration was confined primarily to the ipsilateral LRN and all three divisions of the nucleus were involved. Maximum degeneration was observed in the caudal regions of the parvocellular division. The magnocellular division, except for the extreme dorsomedial area, showed substantial degeneration as well. The subtrigeminal division throughout its entire length contained only sparse degeneration.Electron microscopic examination following spinal cord lesions revealed both round and pleomorphic-vesicle terminals in various stages of electron dense degeneration. The majority of the degenerating terminals were of the round-vesicle variety. Both types of terminals contacting somata were also observed to degenerate but their number was small in comparison to those on dendritic profiles. Terminals in synaptic contact with two dendritic profiles were also observed to degenerate. Some of the large terminals belonging to synaptic configurations (glomeruli) underwent degeneration and were therefore of spinal origin as well.     

雌激素对大鼠红核神经元保护作用的体视学定量

目的 观察雌激素（E₂）替代治疗对去卵巢SD大鼠脊髓损伤后红核神经元逆行性损伤的影响。方法 成年雌性SD大鼠80只, 随机分为正常组、红核脊髓束(RST)损伤组、E2替代治疗组、雌激素受体拮抗剂（ICI）治疗组和E₂+ICI联合治疗组。SD大鼠去势后1周采用选择性切断脊髓C3～C4左侧背外侧索制作单侧红核脊髓束（RST）横断损伤模型,给予不同条件治疗后1周、2周和4周对各组大鼠采用前肢支撑探测实验进行行为学评价,用红色荧光金（FR）逆行荧光示踪及体视学定量分析法,观察红核神经元的形态及数目变化。结果 前肢支撑探测实验结果显示,各时间点E2替代治疗组的左前肢使用率均高于除正常组外其他各组,但无统计学意义（P >0.05）;形态学检测结果可见各组大鼠中脑右侧FR阳性红核神经元数目除正常组外均有不同程度减少,尤以4周时最为明显。E2替代治疗组右侧中脑FR阳性红核神经元与RST损伤组、ICI治疗组和E₂+ICI 联合治疗组相比胞体饱满、轮廓清晰、突起长,体视框计数结果显示,E₂替代治疗组红核FR阳性神经元数目明显多于其余各组（P<0.05）,但RST损伤组、ICI治疗组和E₂+ICI联合治疗组之间右侧中脑FR阳性红核神经元数目未见明显差异（P>0.05）。结论 大鼠脊髓横断损伤后中脑红核神经元发生逆行性损伤,E₂替代治疗可减轻脊髓损伤引发的继发性红核神经元损伤。     

The central cervical nucleus in the cat. II

Summary After HRP injections in kittens and adult cats into parts of the cerebellum known to receive spinal afferents, retrogradely labelled neurones were found in the C1–C4 segments of the spinal cord, primarily in the central cervical nucleus (CCN). A few labelled neurones were also found in laminae IV and VI–IX of Rexed. The results obtained in kittens and adult cats were similar.Control HRP injections were made into the vestibular nuclei and the inferior colliculus. After injections mainly involving the vestibular nuclei a few faintly labelled neurones were found in the C1–C4 segments in, and occasionally also outside the CCN, in laminae VI–VIII. After injections into the inferior colliculus, however, no labelled neurones were observed in these segments.After spinal cord hemisections at C1 and bilateral HRP injections into the anterior lobe, nearly all labelled CCN neurones were found ipsilateral to the hemisections. Labelled axons of such CCN neurones could be traced across the midline to the lateral funiculus. A few neurones were found outside the CCN in laminae VII–IX. Contralaterally labelled neurones were found mainly in lamina VI.Abbreviations b.c. brachium conjunctivum - CN cuneate nucleus - Cr. I, II crus I and II - DV descending (inferior) vestibular nucleus - ECN external cuneate nucleus - i.c.p. inferior cerebellar peduncle (restiform body) - LV lateral vestibular nucleus - MV medial vestibular nucleus - N.d. dentate (lateral) nucleus - N.f. fastigal (medial) nucleus - N.i. interpositus nucleus - N.pr.V principal nucleus of trigeminal nerve - N.V motor nucleus of trigeminal nerve - Ol.s. superior olive - pfl. paraflocculus - pfl.d. dorsal paraflocculus - pmd. paramedian lobule - SC superior colliculus - s.c.p. superior cerebellar peduncle - SV superior vestibular nucleus - Tr.V spinal trigeminal tract - x group x of Brodal and Pompeiano (1957) - I-X cerebellar lobules of Larsell (1953) - I-IX spinal cord laminae (Rexed, 1952)     

Interconnections between the dorsal column nucleus and the cerebellum in a reptile

Interconnections between the dorsal column nucleus and the cerebellum were examined in one group of reptiles, Caiman crocodilus. After anterograde tracer injections into the dorsal column nucleus, efferents terminated nearly exclusively in the white matter and ventral portion of the granule cell layer of the ipsilateral cerebellum. Subsequent to deposition of a retrograde tracer into the cerebellum, neurons in the central and ventral half of the dorsal column nucleus were labeled. When compared with the origin of midbrain and spinal cord projecting cells in Caiman, cerebellar projecting neurons arose from a more rostral location in the dorsal column nucleus than did neurons that terminated in either of these two other targets. The results of the present and previous experiments suggest that the dorsal column nucleus in this reptilian group is organized into sectors based on efferent target in a fashion similar to what has been described in certain mammals. Furthermore, the presence of this circuit in crocodilians and turtles suggests that his pathway from the dorsal column nucleus to the cerebellum arose early in amniote evolution.     

Presaccadic omnidirectional burst activity in the basal interstitial nucleus in the monkey cerebellum

We recorded saccade-related neurons in the vicinity of the dentate nucleus of the cerebellum in two monkeys trained to perform visually guided saccades and memory-guided saccades. Among 76 saccade-related neurons, 38 showed presaccadic bursts in all directions. More than 80% of such burst neurons were located in the area ventral to, not inside, the dentate nucleus, which corresponded to the basal interstitial nucleus (BIN as previously described). We found that the activity of the BIN neurons was correlated with saccade duration but not with saccade amplitude or velocity. Thus, when tested with visually guided saccades, the burst started about 16 ms before saccade onset and ended about 33 ms before saccade offset, regardless of saccade amplitude. The characteristic timing of the BIN cell activity was maintained for different types of saccades (visually guided, memory-guided and spontaneous saccades), which had different dynamics. Although the number of spikes in a burst for each neuron was linearly correlated with saccade amplitude for a given type of saccade, the slope varied depending on the type of saccade. Peak burst frequency was uncorrelated with saccadic peak velocity. In contrast, burst duration was highly correlated with saccade duration regardless of the type of saccade. These results suggest that BIN neurons may carry information to determine the timing of saccades. Received: 14 August 1997 / Accepted: 17 February 1998