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T Pasik

Publications and source records attributed to T Pasik.

At least 37 records · Page 2Linked to original sources
PubMed1981

Extrageniculostriate vision in the monkey. VIII. Critical structures for spatial localization.

Eight monkeys (Macaca mulatta) were trained on a spatial localization task before and after either total ablation of the striate cortices with partial damage to circumstriate cortices, complete colliculus removals, or combined ablations. The lesions were histologically verified. The task, given under normal room illumination, required the animals to reach for a target randomly placed in one of eight equal segments of a while disk located at arm's length. An apple cube, affixed to the center of the target, served as the reward for accurate reaching. A correct response consisted of an initial contact with either the target or the apple cube directly. The animal was trained sequentially to a criterion level of performance set at 90% correct responses over four 56-trial consecutive sessions using black disks of decreasing diameter (i.e., 90 mm, 55 mm, 35 mm, and 15 mm). Finally, only the apple cube, about 10 mm on a side, was presented. Four animals with complete or almost complete bilateral superior colliculus removals were unimpaired in their performances. The other four subjects with total striate cortex removals could be trained to reach accurately for all targets, but with marked deficits on the first and last tests, i.e., the 90 mm disk and the apple cube. When the striate cortex was ablated in the colliculectomized animals, they failed to attain a criterion level of performance in almost 6,000 trials. These results indicate that the superior colliculus is at least one structure that is critical for spatial localization in the absence of striate cortex, but it is not crucial for this capacity in the otherwise intact animal. In addition, the findings confirmed previous studies which showed that monkeys with total bilateral striatectomies could require the ability to execute accurate visually guided reaches. The present and earlier studies emphasize the primary importance of the geniculostriate system for the function explored and do not support a sharp dichotomy between two independent visual systems in the monkey.

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PubMed1980

Early postnatal development of the monkey neostriatum: a Golgi and ultrastructural study.

Paired specimens of the neostriatum were taken from monkeys at zero (newborn), one, two, four, eight, and 16 weeks of age, and prepared for Golgi impregnations and electron microscopy. Light microscopy shows that in the first postnatal week, the structure contains the five neuronal types and four categories of afferent axons described in the adult, as well as some cells too undifferentiated to classify. Most neurons exhibit immature dendritic features, including local enlargements, terminal growth cones with filopodia, and filiform processes. In spiny type I cells, various levels of maturity may coexist in regions of a single dendrite, in different dendrites of the same neuron, and among individual cells. Spine density increases progressively with age, but the relative distribution of spine types remains about the same. Spiny type II neurons show some decline in spine density, and generally mature sooner than spiny type I cells. The long axons of spiny neurons have varicosities which disappear at about eight weeks. In younger animals (newborn and one week), the dendrites of aspiny neurons (types I, II, and III) may have a "spiny" appearance, exhibiting many spine-like and filiform processes. Concurrently, the short axons vary in degree of arborization from very immature to well developed. Electron microscopy corroborates the developmental features recognized in the Golgi material: dendritic and axonal growth cones, filopodia and varicosities, as well as various stages of maturation in somata and dendrites. Degenerating elements, mostly of an axonal nature, are seen up to eight weeks. The synapses which reach maturity at birth are of the asymmetric axospinous type, in which the axonal profile contains small round vesicles, and of the symmetric axodendritic class, with the presynaptic elements having pleomorphic vesicles. Some synapses are slower to mature and appear at one to eight postnatal weeks. These include those made by profiles with pleomorphic vesicles, forming either symmetric contacts with somata and axon initial segments, or asymmetric contacts with spines. The same applies to the asymmetric axodendritic synapses made by elements containing small round vesicles. Finally, profiles containing large round or flat vesicles are the latest to participate in mature synapses formation. Findings indicate that a considerable degree of qualitative and quantitative change takes place in the monkey neostriatal neuropil during early postnatal development, especially in the first eight-week period.

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PubMed1980

Ultrastructure of Golgi-impregnated and gold-toned spiny and aspiny neurons in the monkey neostriatum.

Golgi-impregnated, gold-toned spiny and aspiny neurons in the monkey neostriatum were deimpregnated and examined at the electron microscope level. Spiny type I neurons have relatively large nuclei with few indentations and aggregates of chromatin under the nuclear membrane which in some regions give the appearance of a dark rim. The small quantity of surrounding cytoplasm is poor in organelles. Aspiny type I neurons have eccentric, highly indented nuclei. The relatively large proportion of cytoplasm is rich in organelles especially Golgi apparatus and rough endoplasmic reticulum which often appears in stacks. Synapses with symmetric membrane densities are common on the somata of spiny type I neurons. Those on the proximal and distal dendritic shafts are few in number and asymmetric, and those on spines more frequent and primarily asymmetric. Aspiny type I neurons have few synapses on their cell bodies. Proximal and distal dendrites, however, are contacted by numerous profiles which contain small round vesicles and make both symmetric and asymmetric synapses. The same axon terminals also synapse with dendritic spines of spiny neurons, indicating that an input, most likely of afferent origin, is shared by both cell types. Other less frequently occurring profiles forming symmetric membrane densities also contact the dendrites of aspiny and spiny neurons. The axon hillocks and initial segments of both neuronal types receive a synaptic input, which is more common on spiny cells. Results offer unequivocal evidence for the differences in the ultrastructure of these two most common categories of medium-size neostriatal neurons, which may help in their proper identification in standard material, as well as information on the types and distributions of synaptic inputs onto these neurons. Moreover, the findings clarify some controversies in the literature probably originating from observations on a mixed population of cells of medium size.

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PubMed1980

Extrageniculostriate vision in the monkey. VII. Contrast sensitivity functions.

1. Psychophysical and electrophysiological experiments have indicated the importance of spatial frequency components and their respective contrasts and orientations for the recognition of patterns. It is in the striate cortex where these types of information first converge, a fact that lends support to the accepted crucial role of this structure in pattern discrimination. 2. Monkeys with total bilateral ablation of the striate cortex, however, retain a residual capacity for pattern discrimination and also can differentiate between a vertical and an oblique luminous bar. The present study explores their capacity for spatial frequency detection both as a function of contrast and, by extrapolation, at maximum contrast (visual acuity measure). 3. Monkeys were presented with a forced choice between a homogeneous target and a vertically oriented sinusoidal grating in a pulling-in apparatus. Stimuli were produced by the transillumination of transparencies at spatial frequencies of 0.5, 1.0, 2.0, 4.0, 8.0, 16, and 32 cycles/deg, in 0.1-log unit steps of contrast from 0.79 to 0.006. The stimuli subtended 8 degrees of visual angle and were matched for mean luminance at 20 cd/m2. After mastering the discrimination of one spatial frequency at the highest contrast, contrast thresholds were first estimated by a staircase technique, and then determined by the method of constant stimuli. The procedure was repeated for each spatial frequency before and after histologically verified total bilateral removal of striate cortex and partial damage to circumstriate cortices. 4. Discrimination at all spatial frequencies was mastered by all normal monkeys. Postoperatively, they could solve only problems with frequencies between 0.5 and 4.0 cycles/deg. 5. Contrast sensitivity (threshold-1) functions for normal and destriated monkeys have the characteristic inverted J shape. The high- and low-frequency limbs are related exponentially to spatial frequency, and the peak of the curve is about 2.0 cycles/deg. The dimensions of the functions, however, change significantly following the ablation. Sensitivity is depressed at all spatial frequencies. The mean "visuogram" indicates a 26-dB flat loss. 6. The mean high-frequency cutoff point is 43 cycle/deg preoperatively and 12 cycles/deg postoperatively, equivalent to 0.7' and 2.5' of arc, respectively. The latter value is not worse than 20/80 on the Snellen chart. 7. The variability of the response at each spatial frequency in the staircase method and the slope of the psychometric function derived from the method of constant stimuli provide a measure of "instability" and "precision," respectively, which are inversely related. Preoperatively, precision is significantly greater at high than at low spatial frequencies. Postoperatively, it is similar at all frequencies, and the values are lower than those determined preoperatively. 8. The results demonstrate that destriated monkeys can detect gratings, although to a lesser degree than normal animals...

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PubMed1979

Downward gaze in monkeys: stimulation and lesion studies.

Ten monkeys were stimulated unilaterally and bilaterally through bipolar electrodes placed stereotactically on each side of the midline under light barbiturate anaesthesia. Bilateral simultaneous stimulation elicited straight downward binocular movements from a core of tissue about 40 mm3 on each side which included the fields of Forel, zona incerta, subthalamic nucleus, oral pole of the red nucleus, fasciculus retroflexus and 'area tegmentalis'. Unilateral stimulation of the same points yielded downward eye movements in only 25 per cent of the instances. Upward deviation of the globes could be elicited by bilateral stimulation of tissue located more caudal, ventral and medial than that from which downward movements were obtained. Bilateral electrolytic lesions within the region outlined above caused significant defects in downward gaze both in saccadic and slow pursuit binocular movements. Passive bending of the head backwards, however, resulted in downward deviation of the globes (oculocephalic reflex). Optokinetic nystagmus and after-nystagmus downward were abolished. Oblique (45 degrees) optokinetic stimulation elicited a perverted response in the horizontal plane. Vestibulo-ocular reflexes elicited by bilateral warm irrigation of both ear canals with the monkey in the erect position, or by turning the animal while lying on one side, caused a strong tonic deviation upward with absence of nystagmus downward. Some of these monkeys showed additional alterations in upward gaze but they were less severe in intensity and duration than those of downward gaze. All eye deviations in the horizontal plane were consistently normal. Recovery occurred in all types of vertical binocular movements except in the rapid motions (saccades and quick phases of nystagmus) below the horizontal meridian. A unilateral lesion had no effect. The minimal damage producing downward gaze defects was about 1.7 mm in diameter, cetred in the prerubral fields, rostral and medial to the red nuclei with minimal involvement of the oral pole of these structures. The nuclei of Cajal, Darkschewitsch and interstitialis of the posterior commissure, as well as the fasciculus retroflexus and the posterior commissure, were spared by this lesion. The so-called rostral interstitial nucleus of the medial longitudinal fasciculus and the nucleus campi Foreli appear to be destroyed. These structures are known to receive an input from the paramedian pontine reticular formation and project on to the oculomotor nerve nucleus. These results demonstrate that the prerubral fields contain structures which are critical for rapid eye movements downward, and therefore an isolated downward gaze palsy is a strong indicator of a bilateral lesion of this zone. The findings in the few reported cases with this sign and available pathological analysis suggest that our conclusions from the experimental monkey apply to man as well. The concept of bilateral innervation for vertical eye movements is amply confirmed for the downward vectors...

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PubMed1976

A Golgi study of neuronal types in the neostriatum of monkeys.

Examination of the nestriatum of monkeys prepared by the Golgi-Kopsch perfusion method revealed the presence of at least 6 neuronal types. The spiny type I is medium size with a high density of dendritic spines. The axon extends well beyond the dendritic field and gives off many collaterals. The spiny type II is either medium or large size, has long thick dendrites with a relatively low density of spines, and an axon similar to that of the previous type but with fever collaterals. The aspiny type I is medium size with varicose dendrites and a thin axon arborizing in the immediate vicinity of the soma. The aspiny type II is large, with many thick and thin varicose dendrites. The aspiny type III is medium size with smooth dendrites and an axon ramifying profusely within the dendritic field. The neurogliform cell is small with many branching processes. Findings indicate that the neostriatum has 2 distinct types of spiny neurons with long axons (spiny I and II), some of which may contribute to the efferent system. There are also 2 (aspiny I and III) or perhaps as many as 4 categories (aspiny I, II, III and neurogliform) of typical Golgi type II cells. Large neurons belong to 2 separate populations, one with dendritic spines and a long axon (large version of spiny II), and one with varicosities and presumably a short axon (aspiny II). A realistic interpretation of neurophysiologic data on the neostriatum must take into account all cell types instead of the current view of considering it as a pool of interneurons with few output cells.

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PubMed1976

Synapses between interneurons in the lateral geniculate nucleus of monkeys.

Electron microscopic examination of the monkey lateral geniculate nucleus, pars dorsalis (LGNd) reveals the occurrence of synaptic contacts between profiles belonging to interneurons (I-cells). Almost all combinations are observed, namely, axodendritic, dendrodendritic, dendrosomatic and somatodendritic, the most frequent being the dendrodentritic synapses between the presynaptic dendrites characteristic of I-cells. Quantitative analysis of 5 samples, each consisting of 200 mum2 of net LGNd neuropil, shows that presynaptic membrane specializations present in I-cell axonal and dendritic elements amount to a mean of 3.73 mum or 8.16% of the surface of such profiles. Only 61% of this extent is in contact with principal cells (P-cells), and an unexpectedly high 39% engages other I-cell profiles. A tentative segregation of axonal and dendritic endings revealed the following significant mean differences: dendritic terminals are more numerous and larger; axonal profiles have more of their surface occupied by synaptic sites and each contact is longer. Findings suggest the existence of a network of interconnected interneurons which are presumably inhibitory in nature. Such an arrangement can provice a certain measure of anisotropic disinhibition which may be responsible for specific transformations occurring in the LGNd depending upon the size and velocity of the stimulus as well as of the degree of synchronicity of temporal patterns.

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PubMed1975

A comparison between two types of visually-evoked nystagmus in the monkey.

Similarities between optokinetic nystagmus (O.K.N.) and flicker-induced nystagmus (F.I.N.) include: response buildup and occurrence during the entire period of stimulation; absence of habituation; after-nystagmus in the same direction, occasional after-after-nystagmus to the opposite side; frequency spectrum, peak frequency and existence of lower and upper frequency thresholds. Phenomena are different in that for O.K.N. the stimulus is in motion; binocular and monocular stimulation are effective; direction is determined by direction of motion; unidirectionality is absent; there is minimal influence of background illumination, posture, labyrinthine receptors, and section of crossed optic fibers. For F.I.N. the stimulus is stationary; the response is elicited only by monocular stimulation; the direction is determined by the stimulated eye; there is exclusive unidirectionality; it is abolished by background illumination, optic chiasm section and bilateral labyrinthectomy; it is strongly influenced by posture. This comparison suggests that O.K.N. and F.I.N. are separate responses and that the effective stimulus for F.I.N. may activate selectively the crossed optic fibers.

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PubMed1975

Postnatal differentiation of "presynaptic dendrites" in the lateral geniculate nucleus of the rhesus monkey.

The most characteristic synaptic arrangement in the LGN is the triadic unit, in which a retinal terminal is presynaptic to a principal cell (P cell) and to a Golgi interneuron (I cell) dendrite, which contains synaptic vesicles and is in turn presynaptic to the same P-cell element. The ontogenetic differentiation of these "presynaptic dendrites" was studied in monkey LGN by standard and quantitative electron microscopy. The dendrites and axonal arborization of I cells are well developed in the newborn monkey. Scattered synaptic vesicles are present in the dendrites, but these profiles exhibit only postsynaptic sites. The dendrodendritic synapse of the triadic arrangement is missing, although contacts between P-cell and I-cell dendrites can be observed. Conversely, the I-cell axons in the newborn establish numerous synapses with dendrites and perikarya of P cells. At about 2 weeks of age, presynaptic sites appear in the I-cell dendrites, resulting in the formation of synaptic triads. Parallel to the development of "axonal" properties in the dendrites, the number of true I-cell axonal profiles decreases sharply. These transformations become progressively more frequent with age, and beyond 8 weeks the LGN ultraarchitectonics approaches that of the mature animal. The percentage of the surface of interneuron processes occupied by presynaptic sites is similar at all developmental stages at about the 2.6% level. The relative contribution of presynaptic dendrites and of axons changes, however, so that the actual length of contacts in the mature monkey is only one-half that of the newborn for the axonal sites, and over 50 times longer for the dendritic sites. The correlation of these findings with electrophysiologic and behavioral references suggests that some but not all axonal functions may be taken over by the dendrites, that the possible inhibitory phasing of P-cell discharge would appear only after the second postnatal week, and that the triadic arrangement may not be indispensable for brightness or total luminous flux discrimination but could be required for more complex forms of visually guided behavior.

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