Learning In Rabbits Research Articles

Anterior thalamic discriminative neuronal responses enhanced during learning in rabbits with subicular and cingulate cortical lesions

The neuronal discharge that develops in the anterior ventral thalamic nucleus (AVN) in response to a task-relevant stimulus during learning is enhanced in rabbits with damage in the cingulate and subicular (hippocampal) cortical areas that project to this nucleus. These results indicate that the corticothalamic projections limit the anterior thalamic response but they do not appear to contribute casually to its development. Thus, the discriminative neuronal response is owed to interactions that occur wholly within the subcortical domain of the AVN. The production of this neural code for significant stimuli may be the principal function of the AVN. The enhanced thalamic discharges may be a neural cause of behavioral hyperactivity in animals and amnesia in humans with hippocampal damage.

Effect of substance P on behavior and cortical neuron activity during learning in rabbits

1. In experiments on conscious, loosely restrained rabbits, using a subcutaneously administered undecapeptide, substance P, in doses of 250 μg/kg, behavior and neuron activity was studied in the visual and sensorimotor areas of the neocortex and in the hippocampus during elicitation of the defense reflex conditioned to light flashes and conditioned inhibition. 2. Introduction of sP evoked a short-term loss of motor reactions to the reinforcing stimulus; a lowering in probability of movements to reinforced and inhibitory light flashes; and a prolonged quickening of heartrate and slowing of breathing rate. 3. The background action of sP, among the majority of investigated neurons responding to stimulus presentations, resulted in a fall in background activity and a weakening of excitatory and strengthening of inhibitory response components, especially to the painful reinforcing stimulus. Some neurons showed an increase in excitatory reactions. 4. Bioelectric indicators reflecting a strengthening of inhibitory hyperpolarization processes during internal inhibition were unaffected: inhibitory background pauses and evoked activity in cerebral cortex neurons, together with corresponding slow potential fluctuations, were unchanged by sP.

Cingulate cortical and anterior thalamic neuronal correlates of reversal learning in rabbits.

Unit activity of the cingulate cortex and the anteroventral (AV) nucleus of the thalamus in rabbits was recorded during reversal training following differential conditioning of a locomotory (wheel rotation) avoidance response. The positive and negative conditional stimuli (CS+ and CS-) were pure tones (1 kHz and 8 kHz), and the unconditional stimulus was footshock (1.5 mA). During the first session, activity appropriate to the original task (i.e., a greater neuronal response to the CS- than to the CS+) occurred in the deep cortical laminae (V and VI), but the superficial laminae (I-IV) manifested the original discrimination in certain records and the reverse discrimination in others. All discriminative effects diminished during subsequent sessions except the short-latency (25-msec) deep laminar original discrimination, which persisted throughout reversal training. Activity of the AV nucleus underwent gradual transition, in parallel with the behavior, from the original to the reverse discrimination. Arousal-producing footshocks given after behavioral reversal educed the original and reverse discriminations in the deep and superficial laminae, respectively. These data are interpreted to indicate the role of cingulate cortex and anterior thalamus for encoding the associative significance of the conditional stimuli.

The effect of cutaneous afferent activity on instrumental learning in rabbits

The nictitating membrane response was trained in rabbits by two methods: (a) an instrumental escape-avoidance paradigm, and (b) a yoked classical conditioning paradigm. The magnitude of cutaneous afferent activity (CAA) from the orbital region of the eye was controlled using mechanical and chemical means. Animals received training in both instrumental and classical conditions with augmented and diminished CAA. Diminished levels of CAA were found to depress learning in both training paradigms. Instrumental animals emitted more nictitating membrane responses than did the yoked classical controls under conditions of augmented CAA. It was concluded that the general importance of the role of CAA in learning was strengthened.

Chlordiazepoxide and aversive conditioning: Effects of acquisition and performance of the conditioned nictitating membrane response in the rabbit

A 12-mg/kg dosage of chlordiazepoxide was shown to disrupt acquisition and postasymptotic performance of the classically conditioned nictitating membrane response of rabbits induced by pairing a tone with eyeshock. This result makes more plausible the hypothesis that chlordiazepoxide interferes with avoidance learning in rabbits by suppressing the conditioned fear component of avoidance learning.

Cortical stimulation during learning in rabbits

Rabbits were trained to perform a conditioned avoidance response to a buzzer. Prior to the beginning of training, nonpolarizable electrodes were implanted in the frontal, visual and auditory cortex bilaterally. The effect of cathodal and anodal polarization was tested during the course of training. Cathodal polarization in both the frontal and auditory areas caused a significant decrement in performance, lasting over a period of two days. Cathodal polarization in the visual cortex did not alter the conditioned avoidance response to the buzzer. Anodal polarization produced no consistent effects on performance.