Effect of interruption of the visual pathway on the response to geniculate stimulation

Optic nerve section or destruction of the lateral geniculate nucleus increased the amplitude and elevated the recovery cycle of the cortical response to lateral geniculate radiation stimulation in cats. The lesions may have acted by eliminating tonic inhibitory or occlusive volleys originating in the retina, or both.

Effect of cooling of orbital cortex on exercise hyperpnea in the dog

The significance of cortical contribution to the hyperpnea of exercise has long been debated. An attempt was made to evaluate the role of this factor by cooling the respiratory area of the orbital cortex in 20 experiments on 13 Nembutal-urethane anesthetized dogs before, during and after electrically induced exercise of the hind limbs. Orbital cooling during eupnea produced a 10% decrease in respiratory rate with questionable reduction of minute volume. Cooling induced during exercise resulted in reduction of mean ventilatory volume from 4.37 l/min. to 4.18 l/min. The difference is highly significant statistically and represents 20% of the exercise hyperpnea under these conditions. Cessation of cooling was followed by return to precooling levels. Results indicate that cortical impulses contribute to exercise hyperpnea even under conditions of anesthesia and low levels of exercise and suggest a quantitative approach to evaluation of this factor under more physiologic conditions.

Submitted on July 21, 1958

Antidromic cortical response to stimulation of isolated pyramidal tract

Direct electrical excitation of the intact medullary pyramids evokes a complex cortical response. When the pyramidal tract was dissected away from the bulb and stimulated in isolation. the antidromic cortical response consisted of a simple, positive potential, regardless of the stimulus parameters. This finding necessitates a reinterpretation of previous results obtained by stimulation of the intact pyramids.

Attention units in the auditory cortex

In the course of examining single unit responses from the cortex of unrestrained and unanesthetized cats, we have come upon a population of cells that appears to be sensitive to auditory stimuli only if the cat "pays attention" to the sound source. We have described these responses, since they have not been previously reported and since they illustrate an important difference between the information which can be gleaned from experiments of this type and that obtained in the usual "acute" microelectrode experiment.

Statistical properties of near threshold responses to brief sounds in the MES auditory cortex of the anesthetized dog

Evoked responses to near threshold p pulses recorded with a 50-channel cathode ray oscilloscope from the MES auditory cortex were analyzed statistically. Observations were taken at 3-msec. epochs for approximately 180 msec. Density functions of the evoked potential at these epochs were essentially normal. The average potential from a single electrode consisted of an initial positive followed by a negative component. The correlation coefficient between the positive and negative components was zero suggesting independence. Standard deviation increased during the positive component of a response decreasing to the zero crossing or was followed by a secondary component. Spatially, in the anterior-posterior direction, the average potentials decremented to approximately zero in 2–4 mm. The decrement was less prominent dorso-ventrally. Spatially, the standard deviation showed the same pattern as the mean.

Spread of directly evoked responses in the cat's cerebral cortex

A study has been made of the electrical responses to direct stimulation of the exposed cerebral cortex of cats that had been immobilized with neuromuscular blocking drugs, and whose muscle and skin wounds had been locally anesthetized. The characteristics and spread of the first and second surface-negative responses are described. It was found that the first surface-negative response to weak stimuli decays linearly to zero at 3 to 6 mm. from the point of stimulation. Intermediate stimuli cause farther and non-linear spread: responses are re-initiated, or reinforced, at 6 to 10 mm.; and supramaximal stimulation produces reinforcement both at 5 and at 10 mm. The conduction velocity of these responses is uniform for linear spread (0.7 to 2.0 m./sec.), but reinforced responses occur 1 to 3 msec. earlier than would be expected for simple conduction. The phenomenon of re-initiation, or reinforcement, depends upon the excitatory state of the brain; circulation and previous stimulation are important factors. Connections outside the gyrus matter only in so far as they provide other sources of general excitation. It is concluded that two types of transmission: slow and fast, can lead to generation of similar surface-negative responses. The suggestion is made that the slowly conducted surface-negative potentials are due to direct or to synaptic excitation of pyramidal cells; while the responses with shortened latency are initiated synaptically on other pyramidal cells after fast conduction at about 10 m./sec. in tangential fibres.

The interpretive cortex; the stream of consciousness in the human brain can be electrically reactivated

The interpretive cortex has in it a mechanism for instant reactivation of the detailed record of the past. It has a mechanism also for the production of interpretive signals. Such signals could only be significant if past records are scanned and relevant experiences are selected for comparison with present experience. This is a subconscious process. But it may well be that this scanning of past experience and selection from it also renders the relevant past available for conscious consideration as well. Thus, the individual may refer to the record as he employs other circuits of the brain. Access to the record of the past seems to be as readily available from the temporal cortex of one side as from that of the other. Auditory illusions (or interpretations of the distance, loudness, or tempo of sounds) have been produced by stimulation of the temporal cortex of either side. The same is true of illusional emotions, such as fear and disgust. But, on the contrary, visual illusions (interpretations of the distance, dimension, erectness, and tempo of things seen) are only produced by stimulation of the temporal cortex on the nondominant (normally, right) side of the brain. Illusions of recognition, such as familiarity or strangeness, were also elicited only from the nondominant side, except in one case.

Learning in rats with extensive neocortical damage

Albino rats with as much as 99 percent damage to the cerebral cortex were trained on a position habit in a simple T-maze. The operated rats were found to learn the problem as efficiently as normal animals even when a 30-second delay was imposed between the response and the food.

Carotid and vagal afferents and drug action on transcallosally evoked cortical potentials

The use of transcallosally evoked cortical potentials to study the action of intracarotidly injected drugs on cerebral synapses has necessitated the demonstration that vagal, baroreceptor, and chemoreceptor influences do not play essential roles in the drug effects observed-for example, the cerebral synaptic inhibitory action of serotonin.

Excitation and inhibition of neuronal firing in visual cortex by reticular stimulation

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.

Comparison of direct cerebral and cerebellar cortical responses in the cat

Surface-evoked cerebral and cerebellar responses were compared in 35 cats. Single stimuli and 1-second trains (6 and 20/sec.) were used. Effects of gamma aminobutyric acid (GAB) applied to the cortical surface and of Nembutal and procaine injected intravenously were studied. Response of cerebral cortex to a single shock shows at least four components: initial negative spike, second negative wave, after-positivity, and slow negativity. Cerebellum shows only the initial negative spike and the slow negativity, second negative and after-positivity components being absent. In both cerebrum and cerebellum slow negativity shows summation with serial stimulation. Application of GAB to the cerebellar surface causes replacement of the negative spike by a positive one and a concurrent reduction in amplitude of slow negativity. In cerebral cortex Nembutal produces a striking augmentation of singly or serially evoked slow negativity, but marked amplitude reduction or reversal to positive polarity of the serially evoked primary spikes. By contrast procaine abolishes summed slow negativity of cerebral cortex leaving serial spikes unaffected. In the cerebellum Nembutal and procaine have no effect upon the direct cortical response at dosage sufficient to produce cerebral alterations. Thus synaptic activity signaled by the responses studied appears to be more susceptible to Nembutal and procaine in cerebrum than in cerebellum.