Date of Award
Doctor of Philosophy
Joel F. Lubar
Stephen J. Handel, William J. Davis, Jasper M. Brener
The literature dealing with the behavioral effects produced by ablation of the septum, frontal cortical areas and the hippocampus is reviewed. It is concluded that the medial septum, the dorsolateral frontal cortex (and its analogue in lower forms e.g., gyrus proreus in the cat and precollosal midline cortex in the rat) and the dorsal hippocampus form a nodal point within a larger neuronal system that is involved in response regulation.
A model, describing the response regulatory processes mediated by this fronto-cortical-limbic system is proposed, Motor programs are written in the frontal cortex and temoorarily stored in hippocampal area CA3. Feedback stimuli (both internal e.g., proprioceptive, and external e.g., reinforcement) consequent to response initiation are compared with the initial motor program in hippocampal area CA1. If the feedback information matches with the expected outcomes dictated by the motor program, the response sequence is terminated, If comparator deviations arise, the frontal cortical areas are signalled ot error via septo-hippoecampal-entorhinal pathways and a new motor program is written. The role of proprioceptive feedback in response control is emphasized. Hippocampal theta activity is postulated to be a consequence of comparation.
An experiment was conducted in order to assess the effects of frontal (proreal) or septal damage on the ability of cats to acquire response control consistent with efficient performance on a DRL 40 second schedule of reinforcement. Available evidence (Laties, et. al., 1969; Kramer and Rilling, 1970) suggests that efficient DRL performance depends upon the organization and maintenance of collateral behaviors, which in turn facilitate timing behavior by pacing the temporal interval between responses. It is therefore proposed that frontal or septal ablation should impair DRL performance (when meaningful exteroceptive stimuli are lacking) by disrupting the neural mechanisms involved in the analysis of proprioceptive information derived from collateral responses. The experiment was conducted in three stages. During acquisition (30 days) no exteroceptive stimuli were available to signal the end of the required delay. Following acquisition fifteen days of DRL 40 with feedback (a red cue light indicates the termination of the required delay) was instituted. The feedback condition was followed by fifteen days of feedback withdrawal, during which the cue light was no longer used.
Damage to the anteromedial septum and diagonal band, or damage to gyrus proreus, which included its ventral sector, severely impaired the performance of cats during DRL acquisition. The deficit was ameliorated during the feedback period, but reasserted itself when the cue was no longer available. In addition, the shapes of the IRT histograms (indicative of patterns of responding) generated by the septal and proreal cats during the periods of acquisition am withdrawal were significantly correlated with each other, but not with the histograms genera ted by normal and opera ted controls. During the feedback period all histograms were related. Collateral behavior was evident in all animals during the period of acquisition am withdrawal, but was greatly reduced during the feedback period.
It is concluded that efficient DRL performance is dependent upon the utilization of response produced cues derived from collateral behavior, and that damage to the septum or the gyrus proreus impairs the utilization of such cues.
Numan, Robert, "The Effects of Frontal and Septal Ablation on Response Regulation in the Cat. " PhD diss., University of Tennessee, 1972.