Drive discrimination in rats following amygdaloid lesions

Abstract

Amygdaloid and control Ss were compared on their ability to utilize hunger-and thirst-related cues to guide positional responses in a Tvmaze. Amygdaloid Ss performed quite accurately when responding to hunger-related cues, but were deficient when responding to thirst-related cues. This difficulty was mirrored by increased amygdaloid VTE behavior on water-deprivation, but not food-deprivation, trials. It is suggested that the amygdaloid lesions either reduced the effectiveness of the water reward or reduced 8's ability to employ thirst-related stimuli to guide positional responses.Recently, McGowan, Hankins, and Garcia (1972) have suggested that portions of the limbic system, including the amygdala, are importantly involved in the association of internal with external cues. The primary data suggesting such an interpretation is the difficulty experienced by amygdala-damaged animals in associating a novel taste cue (e.g., saccharin) with LiCL or Xdrradiation-Induced illness (McGowan et al, 1972;Kemble & Nagel, 1973;Rolls & Rolls, 1973). Other data, however, are also amenable to such an interpretation. Pellegrino and Clapp (1971), for example, found that basolateral amygdaloid lesions disrupt uncued, but not cued, DRL performance. The authors suggest that this deficit may arise from a difficulty in utilizing proprioceptive information to guide operant responses in the uncued condition. The well-documented passive avoidance deficits following amygdaloid damage (e.g., Pellegrino, 1968 ;Ursin, 1965;, Thompson & Schwartzbaum, 1964) as well as the failure of such animals to adjust running speeds normally to altered magnitude of reward (Kemble & Beckman, 1970a) or to alter open-field activity in response to food deprivation (Kemble, unpublished) may . also be interpreted in a similar way. It should be noted, however, that few of the above studies were designed to test the efficiency of such cue utilization. Ittherefore seemed of interest to explore further the effects of amygdaloid lesions on an animal's ability to utilize internal cues in guiding its behavior. In the present experiment, amygdala-damaged and control Ss were compared in their ability to use cues accompanying hunger and thirst to guide a positional response to an appropriate goal object. METHOD Subjects and Surgical ProcedureThe Ss were 15 male albino rats (Holtzman Co.), weighing 288-325 g at the time of surgery. These animals had previously served in an investigation of home-eage food and water At the conclusion of testing, experimental Ss were intracardially perfused with isotonic saline followed by 10% Formalin solution while deeply anesthetized. The brains were then removed, frozen, sectioned at 24 microns (coronal plane) , and stained with cresyl violet for histological examination. ApparatusTesting was conducted in an enclosed single-unit T-maze constructed of v..·in. plywood, painted flat black throughout, and covered with clear Plexiglas. The startbox was 8 x 5v.. in., the stem 47 x 3% in., and each arm 8~x 4 in. Each goalbox was 12v.. x 5v.. in., ...