The interpeduncular nucleus and retention in albino rats.

Abstract

A recent study has shown that damage to the interpeduncular nucleus (IPN) of the midbrain abolishes a previously formed brightness discrimination habit in rats (Thompson & Massopust, 1960). That this nucleus seems to be implicated in visual performance rather than the adjacent midbrain structures (red nucleus, medial lemniscus, oculomotor nucleus, mammillary peduncle, mammillo-tegmental tract) is indicated by two lines of evidence. First, lesions placed immediately lateral, superior, or posterior to the IPN are without effect on retention. In the second place, the degree of memory loss in percentage of error savings was found to be highly correlated with the extent of damage to the IPN (rho = .85).The present study reports the results of three experiments which were designed to provide further information concerning the role of the IPN in retention. In Experiment 1, an attempt was made to determine whether damage to the IPN impairs retention of a brightness discrimination when the hunger motive is employed. The initial report by Thompson and Massopust utilized avoidance of shock to the feet as a motive. Experiments 2 and 3 were aimed at ascertaining whether or not the IPN functions in memory of nonvisual habits. Two different problems involving different sense modalities were investigated. In one, rats were trained on a kinesthetic discrimination in an incline box (Experiment 2), while the other involved conditioning rats to make a jumping response to the onset of a buzzer (Experiment 3).

Brainstem reticular formation lesions: Amnestic effects on learned habits in the rat

“…8 compose the general memory system of the brain. This is suggested by the findings that the only lesions which impair retention of visual discrimination habits, a kinesthetic discrimination habit, and an avoidance conditioned response to either auditory or visual signals distribute themselves within the foregoing brainstem areas (Thompson, Duke, Malin, & Hawkins, 1961;Thompson, Lukaszewska, Schweigerdt, & McNew, 1967;Thompson et aI, 1964). Additional support for this notion comes from two studies recently completed at the Louisiana State University laboratory.…”

Deficits in position reversal learning following lesions of the limbic system.

“…A single unit enclosed T maze adapted to permit S to escape from electric shock to the feet was used. A complete description of this apparatus is given elsewhere (Thompson, Duke, Malin, & Hawkins, 1961). The distinguishing feature of this apparatus was that the start box and the arms of the T had a grid floor.…”

A discrete interpedunculo-central tegmental region critical for retention of visual discrimination habits in the white rat.

“…There is considerable disagreement concerning the importance of the interpeduncular nucleus (IPN) and the overlying central tegmentum (CT) in the maintenance of visual discrimination habits in the white rat. For example, the results of early lesion studies (Thompson, Duke, Malin, & Hawkins, 1961;Thompson & Massopust, 1960) suggested that the IPN rather than the CT plays a significant role in supporting the performance of a brightness discrimination habit. More recently, however, lesions of the CT have been reported to impair retention of visual discrimination tasks (Hatton, 1965, Thompson, 1963, 1969Thompson, Rich, & Langer, 1964).…”