Sec Stimulus Research Articles

Conditioned responses of hippocampal and other neurons

Changes in the firing rates of neurons in various subcortical structures induced by application of a 1 sec auditory stimulus were recorded in unrestrained animals during movement-free intervals. Pseudo-conditioning trials (500) were followed by conditioning trials (300). During the latter, a food pellet was presented to the animal by a dispenser after every stimulus, provided there was no detectable movement during the stimulus period. The difference between the response rates before conditioning and after conditioning was considered to be a measure of the effect induced by the conditioning procedure. 1. 1. Except for the early response in the dorsal reticular formation, responses consisting of incremental firing rate were increased in size and number and decremental response were attenuated or reversed. Even in the dorsal reticular formation the neuronal activity rate during the last half of the stimulus was augmented. 2. 2. Before conditioning an increment in the firing rate of neurons appeared in most areas during the first 300 msec of stimulation after which the firing rate returned almost to control levels or even systematically below control levels in some areas. In most cases, conditioning procedures caused the early increment to be augmented and the neuronal rate to stay elevated above control levels during the remainder of the 1 sec stimulus (thus reversing the decremental tendency where it had appeared). 3. 3. Incremental changes were largest in hippocampus. These changes were, on the basis of deductive arguments, considered to be independent of skeletal and attentional components of the conditioned response on the one hand, and unrelated to sleep and waking or inhibitory processes on the other. It seemed possible therefore that the changes might be related to a short term or temporary trace of a motivationally significant event.

Prolonged heart rate changes following brain septal stimulation in the unanesthetized cat.

Summary Heart rate changes with septal stimulation were studied in six unanesthetized cats with chronically implanted electrodes. Effects of stimulating mesencephalic reticular formation (MRF) were investigated in four animals. Septal and MRF stimulation at 300 per sec for 2 sec regularly produced cardio-acceleration; septal effects tended to be slower in onset and greater in magnitude. Septal stimulation at 5 per sec for 10 sec produced cardiac deceleration. Variation of stimulus parameters also indicated that weak stimuli caused deceleration and intense ones caused acceleration. Cardio-acceleratory effects of 2 sec of intense septal stimulation were relatively prolonged, generally lasting more than 15min. Repetition of the 2 sec stimulus at hourly intervals appeared to produce a summation of effects, so that after three stimulus trains there was little return to pre-stimulus heart rate. The direction of heart rate change with septal stimulation in the unanesthetized cat appears to be a function of stimulus strength. Cardio-acceleration occurs with strong stimuli in contrast to the deceleration found by others in anesthetized animals.

Effect of task complexity and stimulus duration on perceptual-motor performance of two disparate age groups.

Abstract This study was concerned with two task dimensions, complexity and stimulus duration, which previous research had shown to accentuate or reduce performance. differences between age groups. Young and old groups made an unguided movement at the onset of one stimulus light in a four-light display. Task complexity was varied by altering the number of response alternatives (1 or 2) while holding the display constant. Two stimulus durations were used: 0110 sec and 2.0 sec. Old subjects reacted 30 per cent slower and moved 7G percent slower than young. Both reaction time and movement time were slower for the complex task than for the simple. The difference between simple and complex movement time was significantly greater for old subjects than for young./ Young subjects moved faster with the 0.110 sec stimulus while old subjects moved faster with the 2.0 sec stimulus.

Duration of Angular Acceleration and Ocular Nystagmus from Cat and Man: I. Responses from the Lateral and the Vertical Canals to Two Stimulus Durations

Recordings of ocular nystagmus were obtained from a group of cats and a group of human subjects to 4°/sec2 angular accelerations of 8.4 sec and of 36 sec duration. Lateral canals and vertical canals were stimulated on separate trials. Results showed that the output of both primary and secondary nystagmus was greater for lateral canals. In cats, both lateral- and vertical-canal responses to the 36 sec stimuli peaked after 15–21 sec of angular acceleration and this was followed by a steady decline. Declines were not apparent in nystagmus of human subjects. A further test of these findings was conducted by manipulating arousal variables; human subjects were given special tasks and cats received d-amphetamine. Essentially the same results were obtained as described above. Other differences between the two groups were noted. Cats consistently demonstrated secondary nystagmus whereas humans did not. After termination of acceleration, primary nystagmus from cats lasted longer and exhibited a greater number of eye movements following the 8.4 sec stimulus than following the 36 sec stimulus; this consistency was not evident in humans. However, for humans the sensation of motion following termination of acceleration was of longer duration for the 8.4 sec stimulus than for the 36 sec stimulus. In this regard, nystagmus from cats resembled the subjective reactions of man more than they did the nystagmus of man.

The origin of the post-tetanic hyperpolarization of mammalian motor nerve terminals.

1. Motor nerve terminals in magnesium-poisoned rat hemidiaphragm-phrenic nerve preparations in vitro were stimulated with short depolarizing pulses of approximately threshold strength and the evoked antidromic responses recorded from the phrenic nerve. The percentage of these 1/sec or 0.5/sec stimuli to which there was no antidromic response was used as a quantitative measure of the terminal excitability. After standard tetanic stimulation (1000 impulses at 100/sec) the excitability of the terminals was depressed for an average duration of 60-70 sec, during most of which time no antidromic responses to stimuli of pretetanic intensity were recorded. There was no significant interaction between stimuli to the terminals at rates of 1 or 0.5/sec.2. Potassium-free solutions at first increased, then decreased, the post-tetanic depression of excitability. Raising [K](o) threefold (15 mM) abolished the post-tetanic depression and often converted it to an exaltation of excitability.3. Polarizing currents were applied to the terminals with a second electrode. Depolarizing currents increased, while hyperpolarizing currents decreased, the post-tetanic depression of excitability.4. In solutions with 70% of the normal NaCl content replaced by sucrose, the post-tetanic depression of excitability was reversibly prolonged.5. In the presence of 7.7 x 10(-6)M digoxin or 0.42 mM ouabain there was a small reversible reduction of post-tetanic excitability.6. After exposure to solutions containing no glucose or to solutions containing 3-5 mM sodium azide the excitability of the terminals was not altered by the tetanus. After washing with the control solution, post-tetanic depression of excitability returned. Antimycin-A (1.8 x 10(-6)M) had little or no effect upon post-tetanic excitability.7. It was concluded that the post-tetanic depression of excitability reflected hyperpolarization of the terminals and that this hyperpolarization was caused by a shift of the membrane potential towards the potassium equilibrium potential because of an increase in potassium permeability.