Baruch Blum

Eye movements induced by electrical stimulation of the frontal eye fields of marmosets and squirrel monkeys

Two or three sites in the region of the frontal lobe of marmoset and squirrel monkey are definable as frontal eye fields (FEF) on the basis of electrical stimulation which results in slow and/or saccadic eye movements. In the squirrel monkey these are located on the banks of the arcuate and principal sulci; in the marmoset at estimated analogous locations. Eye ball deviations result from stimulation of these sites with a return to initial position at the end of stimulation. The induced eye movements included large, slow eye movements of varying speeds, micro- and macro-saccades, pendular eye movements, and saccadic stairways. The direction of these eye movements depended on the site stimulated. Both smooth slow and saccadic eye movements were obtained even with stimulation of the same site, depending on the stimulus intensity and the depth of anesthesia. A precise relationship between the site stimulated and the type of eye movement elicited could not be established in these species. Effective stimulus was 300 Hz frequency, 0.2-0.5 ms pulse duration, 0,05-0.05 mA current, and trains of 4-160 pulses. Characteristically, sites for induction of saccadic eye movements were frontal to sites for induction of slow eye movements.

Coordinate frame for pattern recognition in unilateral spatial neglect

The present research examines the effect of spatial (object-centered) attentional constraints on pattern recognition. Four normal subjects and two right-hemisphere-damaged patients with left visual neglect participated in the study. Small, letterlike, prelearned patterns served as stimuli. Short exposure time prevented overt scanpaths during stimulus presentation. Attention was attracted to a central (midsagittal) hation point by precuing this location prior to each stimulus presentation. Minute (up to 1.5 of visual angle) rightward and leftward stimulus shifts caused attention to be allocated each time to a different location on the object space, while remaining in a fixed central position in viewercentered coordinates. The task was to decide which of several prelearned patterns was presented in each trial. In the normal subjects, best performance was achieved when the luminance centroid (LC; derived from the analysis of low-spatial frequencies in the object space) of each pattern coincided with the spatial position of the precue. In contrast, the patients with neglect showed optimal recognition performance when precuing attracted attention to locations within the object space, to the left of the LC. The normal performance suggests that the LC may serve as a center of gravity for attention allocation during pattern recognition. This point seems to be the target location where focal attention is normally directed, following a primary global analysis based on the low spatial frequencies. Thus, the LC of a simple pattern may serve as the origin point for an object-centered-coordiate-frame (OCCF), dividing it into right and left. This, in turn, serves to create a prototype description of the pattern, in its own coordinates, in memory, to be addressed during subsequent recognition tasks. The best match of the percept with the stored description may explain the observed advantage of allocating attention to the LC. The performance of the brain- damaged patients can be explained in terms of neglect operating in the OCCE

A pharmacological analysis of autonomic pathways mediating myocardial disturbances originating in a lateral hypothalamic area of the cat

A study was made of the mechanisms mediating autonomic changes resulting from stimulation of a site in the lateral hypothalamic area (LHA). This site, when stimulated, induced angina-like ECG disturbances similar to those observed in some cases of brain traumas. These ECG changes were often associated with other autonomic changes, such as pressor response, tachycardia (in some cases bradycardia), nictitating membrane (NM) contraction and pupillary dilatation. Most symptoms were sympathetic: they were largely abolished by spinal cord section between C1 and C2, but were not affected by vagotomy, except that bradycardia was converted to tachycardia. Adrenal catecholamines were not involved since adrenal vein ligation was without effect. Hexamethonium (5-10 mg/kg) prevented pressor response and tachycardia in most cats but only partly protected against ECG changes and NM contractions. Atropine methyl nitrate (0.2 mg/kg) abolished the remaining ECG abnormalities and NM tension. The beta-receptor antagonists, propranolol and practolol (50 micrograms/kg) completely prevented the ECG changes induced either by isoprenaline or LHA stimulation. It is concluded that the symptoms induced by LHA stimulation result from noradrenaline release in the target organs.

Facilitation of pattern recognition by cuing foveation with the luminance centroid as origin of the frame of reference

The strategy for visual information processing must vary with the specific situation. We assume that in recognition of pre‐learnt letter‐like patterns under time‐pressure conditions, mechanisms of selective intention arc involved. We propose that, with simple stimuli, foveation is to the luminance centroids of such patterns, and if normally the latter has to he computed by the brain, cuing such information should improve performance. This assumption was tested on three subjects with live stimuli. In confirmation of the working hypothesis, we found significant improvements in performance (p= 0.01 or better) for each of the stimuli, with cuing to ‘relevant’ as compared with ‘irrelevant’ sites, and also when the point of foveation was nearer to the ‘nodal’ site. It is concluded that in pattern recognition processes, nodal regions are computed, the luminance centroid for example, for simple pattern stimuli.

Sympatho-inhibitory mechanisms acting at sympathetic ganglia to attenuate hypothalamic-induced pressor effect in the cat

Pressor and tachycardic effects induced in the cat by stimulation of a lateral hypothalamic (LH) site, are shown to be mediated by sympathetic ganglia nicotinic receptor, and potentiated under atropine methyl nitrate sympathetic ganglia blockage. It is postulated that a sympatho-inhibitory pathway muscarinic ganglionic mechanism, co-activated by the LH stimulation, attenuates the pressor and tachycardic effects, the potentiation presumably being a manifestation of blockage of that mechanism.

Stereotaxic head restraint for chronic and semi-chronic marmoset and macaque monkeys.

A device allowing head holding and stereotaxic manipulations in both small-sized Marmoset and in relatively large Macaca monkeys is described. Its design permits free access to most targets in the visual system and optimizes presentation of visual stimuli in awake-chronic and anaesthetized semi-chronic preparations. Extra-aural attachments to temporal bone are implanted stereotaxically, under anaesthesia, on both sides of the skull. This provides means for stereotaxic head-holding which minimizes discomfort to the animal. Maintenance of stereotaxic precision over long periods of time, possibility of realignment and use of one device for various monkey species are special features of the method.

Logic operations in the central nervous system-implications for information transfer mechanisms

Extracellular unit recordings were derived from the cat sensorimotor cortex by means of tungsten microelectrodes. Evidence was obtained for the value of time-locking of impulses: a critical time interval was demonstrated as essential for modifications caused in putaminally-evoked cortical local field potentials by preconditioning stimuli delivered to the nucleus entopeduncularis. A correlation analysis was carried out on responses of neurones of the sensorimotor cortex to stimulation of the pyramid or of sensory area S1. Differentiation was made between common input and sequential firing operational conditions. Logics of and-gate and of conditional or-gate were recognized. Micro-circuitry was offered in each case. Evidence was offered for the importance of collaterals in such actions.

Organ-localized hypothalamic-stimulated vasculature changes in the cat

Stimulation of specific lateral hypothalamic targets in a cat model induces vascular and/or cardiac changes. Evidence is presented that these may consist of discretely localized sympathetically mediated changes taking place in just one or two organs. Morever, following stimulation of either one of two adjacent lateral hypothalamus sites, pressor effects are induced that superficially look similar, but prove to be mediated by different pathways. To investigate possible synapsing at sympathetic ganglia, e.g. in superior cervical or stellate ganglia, 50 µg atropine methyl nitrate, a ganglionic blocker, was applied directly to the ganglia. This was shown to potentiate the pressor effects, in some cases when applied to the superior cervical ganglia, in others to stellate ganglia, presumably by blockade of a ganglionic attenuating mechanism. The contributions made by different sympathetic nerves to the lateral hypothalamus-induced pressor effect were analysed. Stimulation of one of the lateral hypothalamus sites (TAR.I) in eight cats induced a pressor effect that was abolished by severing a nerve branch, from the superior cervical ganglia laterally, shown to innervate neck muscle vasculature. In another group of nine cats stimulation of TAR.II induced a pressor effect abolished by cutting a branch from the superior cervical ganglia medially, shown to be destined to the vasculature of pharyngeal muscles and possibly lower respiratory tract. The hypothesis that central control via the sympathetic nervous system is responsible for differential organ specific regulation of blood flow to individual organs is discussed.

Rates of nerve impulse propagation as output characteristics — a study on pyramidal tract neurones of cat and monkey

Conduction velocities of PTNs were compared in the cat and in the squirrel monkey. In the cat these were found to be mostly between 40 and 100 m/sec while in the squirrel monkey a wider range of 10 to 120 m/sec was found. An accurate definition of PTN including for slow-conducting cells achieved by the use of as many as five criteria for such definition: spike shape, constancy of response and of latency value, response to high rates of stimulation of over 50/sec, and collision.After achieving the above definition the collision technique was used in a novel way in order to assess probabilities for impulse propagation into the axons of these neurones. Two types of propagation were thus defined qualitatively: a firm and an imtermittent one. The theory was advanced that the latter type of propagation might be related to a stochastically-based process by which the pyramidal tract utilizes the large number of fibers participating in the conduction of signals through it to correct for the signal error intrinsic to single fiber action.

Responses to colour of neurones in area 7a of the inferior parietal lobule of the rhesus monkey

A single-unit study on area 7a of alert, fixating rhesus monkeys revealed responsiveness to primary colours comparable to white light responsiveness shown in other cells. Mostly decremented, some biphasic, and a small portion with incremented neuronal firing response were observed, following stimulation of cells by parafoveal receptive field, rectangular, approximately 20 degrees x 20 degrees red, green or blue-violet light stimuli. The same cell showed no response to white light. Receptive fields of these colour-sensitive cells, like those of white-sensitive cells, were mostly contralateral, some ipsilateral and a few in both hemifields. Augmentation of responses following preconditioning electrical stimulation of lateroposterior-pulvinar targets was observed as with the white-light sensitive cells. It is noteworthy that this monkey area 7a colour sensitivity is complementary to previously demonstrated white light sensitivity. The specific properties revealed by these cells suggest separate channels within area 7a for colour and for achromatic light, the colour sensitivity possibly relevant when chromaticity is of generalized import, and these may subserve the animals orienting response to colour appearance in the near-periphery visual field.