Search

Monkeys were trained to perform a delayed response (DR) task. A visual cue—placement of food under one of two test objects—was succeded by a delay of 18 sec, during which the test objects were concealed and out of reach. At the end of the delay, the objects were made accessible for choice and, if the choice was correct, for reward. Single unit activity was recorded from thalamic nuclei during DR performance. The parvo- and magnocelularis portions of the nucleus medialis dorsalis (MD) were principally explored. Units spontaneously exhibiting rhytmic firing were commonly observed, particularly in MD pars magnocellularis. According to temporal patterns of firing frequency changes during DR trials, 6 different types of units were distinguished. Approximately one-half of all the units sampled in MD, pars parvocellularis, showed sustained elevations of discharge during the delay. These findings are comparable to those made in a separate study of the prefrontal cortical area to which MD, pars parvocellularis, is connected. The firing changes correlated with the behavioral task are interpreted as manifestations of a functional involvement of MD, together with the prefrontal cortex, in DR performance. The possible nature of this involvement is discussed in relation to the available evidence from anatomical, electrophysiological and behavioral research.

The spike activity of single units of the thalamus was explored during hypothermia of dorsolateral prefrontal cortex in monkeys trained to perform a delayed response (DR) task. Lowering prefrontal temperature to 15–20 °C — measured subdurally — induced a profound and reversible deficit of DR performance and a concomitant alteration of firing in cells of the parvocellular portion of the nucleus medialis dorsalis (MDpc). Spontaneous firing frequency was diminished in most of the units affected, while a tendency to grouped, rhythmic discharge was generally accentuated. The normal firing patterns related to DR performance were modified by prefrontal cooling in 63% of the units examined in MDpc. Prefrontal cooling induced a disruption of the sustained elevations of discharge shown by certain types of units during the delay period of DR trials. Sustained activation was attenuated, abbreviated or converted into a paradoxical inhibition as a result of cooling. The effects of prefrontal cooling on behavior and on unit activity in medialis dorsalis are discussed in the context of what is known about input and output connections of the prefrontal cortex. It is apparent that cryogenic depression of this cortical region interferes with the normal neural processes that constitute the substrate of short-term memory function.

The production of alterations in cardiac function by stimulation of diencephalic regions has been reported in the past. These alterations have been considered indicative of the existence of central regulatory mechanisms acting upon the contraction of the heart muscle. The principal purpose of the present study was to clarify further some aspects of this functional relationship. The experiments were carried out in cats under the action of a curarizing agent. Electrodes were stereotaxically oriented to stimulate, in a point-to-point exploration, the ventral structures of the diencephalon. Diencephalic influences upon the heart cycle are revealed by the analysis of the electrocardiogram under stimulation of hypothalamic and subthalamic areas. Changes in rhythm, as well as changes in the configuration of the electrocardiographic wave components, are obtained by stimulation at a number of locations. Effects of sympathetic activation, such as tachycardia and increase in the amplitudes of the QRS complex and the T wave, are much more commonly and consistently seen than those resulting from activation of the parasympathetic system. A zone is delimited from which influences on the heart are most readily exerted. This zone covers most of the lateral and posterior hypothalamus, the zona incerta, and the tegmental fields of Forel. Excitation of these areas frequently results in the activation of abnormal foci of impulse formation in the myocardium.

Nerve cells in the monkey's prefrontal cortex and nucleus medialis dorsalis of the thalamus show changes of firing frequency associated with the performance of a delayed response test. Most cells increase firing during the cue presentation period or at the beginning of the ensuing delay; spike discharge highler than that in intertrial periods is present in some cells throughout the delay. These changes are interpreted as suggestive evidence of a role of frontothalamic circuits in the attentive process involved in short-term memory

The woodpecker is an experiment in Nature, a model for the investigation of mechanisms of basic importance for head injury and its prevention. A preliminary anatomical study of the woodpecker's head suggests that it may be fruitful to explore impact protective systems which are radically different from those in common use.

The frequency of action potentials of about one-third of the neurons sampled in the striate cortex of awake rabbits was clearly modified by mild stimulation of the reticular core of the brain stem. Reticular stimulation often brought about enhancement of firing in units activated by light, while it usually had the contrary effect upon light-inhibited units.

Summary.--Cryogecic probes were implanted in monkeys for cooling cortical "association areas" in unanesthetized state. Cooling was obtained by attaching special D.C. operated thcrmodes to the probes. When the parastriate and the lateral frontal cortex were cooled to 5" C, the amplitude of averaged visual evoked potentials recorded from the striate cortex was depressed. The change is conspicuous in long latency components of evoked response. Experimental hypothermia in a specific sensory pathway constitutes a block for stimuli transmitted along the pathway (3). This study tried to elucidate, by the use of the cooling technique, the influence of association areas of the cortex on responsiveness of the striate cortex to visual stimuli. Three monkeys were used in the experiment. Special thermodes operating on the principle of the Peltier effect, i.e., the heat exchange resulting from the passage of electrical current through a junction of two dissimilar metals (2), were constructed (see Fig. 1A and B) .' A continuous flow of water to the coolers served as a heat sink to the hot side of the junctions while the cold side was applied to one of the brain probes. The gold-plated copper probes (see Fig. lC), shzped to conform to the contour of the cortical surface to be cooled, were surgically implanted under barbiturate anesthesia for subsequent cooling of association cortex. They were placed on the dura and aff~vetl by dental cement to the sur

Recording electrodes were implanted in the lateral geniculate body and striate cortex of rabbits and cats. Primary evoked responses to a brief light flash were recorded from the two locations in the unanesthetized animal. Both at geniculate and cortical levels a power function was found to express satisfactorily in the two species the relationship of response amplitude to illuminance, although a log function generally provided almost as good a fit for the data.

High-speed cinematograph films of a drilling woodpecker were examined by direct visual inspection and by a microdensitometer and computer-imaging technique. These showed (1) that the drilling trajectory is essentially linear, with very little, if any, rotation of the head; (2) that there is minimal movement after impact; (3) that the impact velocity is of the order of 600 to 700 cm/s; and (4) that the impact deceleration is of the order of 1,000 g. Dynamic and morphologic findings in the woodpecker may be highly relevant to the prevention of concussion and brain injury in man. Taken in the context of modern packaging technology and other animal and mathematical modelling research, they suggest that brain injury preventive systems could be greatly improved over those now in common use.