Paul B. Porter

Intracranial Reinforcement Compared with Sugar-Water Reinforcement

Three ways in which electrical, intracranial reinforcement is reputed to differ from conventional reinforcement were tested in an experiment which equated the form of the responses being reinforced and the response-reinforcement relation. Four groups of rats performed instrumental or consummatory responses reinforced by intracranial reinforcement or sugar. In no comparison did the kind of reinforcement produce a difference, but in every comparison the kind of response reinforced did produce a difference. It is inferred that reputed differences between intracranial reinforcement and conventional reinforcement are artifacts.

Effects of restricted rearing on Lashley stand performance.

Rats were reared from weaning to adulthood in either an isolated or enriched environment. Their efficiency at solving a visual discrimination on the Lashley jumping stand and their emotionality were measured as adults. Differences in efficiency of discrimination were slight. Isolated Ss were more timid during the early phases of the experiment but this timidity was reduced by the end of training.

Beta Brain Waves as an Index of Alertness

Reaction times of human subjects are reliably shorter when the signal to respond is given during spontaneous low voltage, fast (beta) brain waves than they are when the signal is given during spontaneous alpha waves. The mean difference of 12 milliseconds is, however, trivial in comparison to the advantage to be expected from forewarning.

OVERNIGHT PERFORMANCE DECREMENT WITH INTRACRANIAL REINFORCEMENT

An overnight performance decrement is allegedly characteristic of habits maintained by intracranial electrical stimulation. The decrement was here found to be (a) not common to all electrode sites, (b) reduced by one un-reinforced trial, and (c) reduced by intracranial stimulation administered below a rewarding intensity. The electrode sites not associated with performance decrement were in the median forebrain bundle (MFB). Those associated with decrement were somewhat removed from the MFB, at sites other experiments have shown to be both positively and negatively reinforcing. These findings are discussed in relation to Deutschs theory of simultaneous drive-induction and reinforcement.

Delayed Punishment of Positively Reinforced Bar Presses

Combining positive and negative reinforcement (both being electrical stimulation of the brain) for lever pressing by 4 rats produced a gradient of suppression as the 2 qualities of reinforcement were separated temporally. Maximal suppression occurred with an interstimulus interval of about 1 sec. This maximum was interpreted as marking the intersection of a waning interaction of the neurological aspects of reward and punishment and a delay-of-punishment gradient. After the 1 sec. of neural interaction, the greater the delay of punishment the less the suppression of responding.

Modification of the autonomic component of the conditioned emotional response.

A series of experiments was conducted to clarify the role of the autonomic nervous system in the acquisition and maintenance of the conditioned emotional response (CER). In Exp. 1 the reactivity of either the sympathetic or the parasympathetic system was altered by drugs during maintenance testing of the CER. 12 rats were trained to bar-press for sugar water on a VI 30-sec. schedule; 6 CER trials were administered during each 2-hr. session. The intensity of the unconditioned stimulus (electric shock) was adjusted for each S so as to suppress responding during the CER signal (tone) to approximately 50% of normal pressing rate. Neither the sympathetic agents (adrenalin, Chlorpromazine, Dibenzyline), nor the parasympathetic agents (methacholine chloride, propantheline, atropine sulfate) reliably altered bar-press rates during the CER trials. Exp. 2 demonstrated that the autonomic agents, in the dosages used, were in fact altering autonomic reactivity as indexed by heart-rate measures. In Exp. 3 acquisition of the CER by 18 rats was found not to be affected by autonomic alteration as produced by drugs.

EFFECTS OF HYPERTHERMIA ON ACTIVITY AND LEARNING

Elevation of body temperature is a common experience. Fevers are the lot of all of us, and heat therapy is almost as ubiquitous (Licht, 1958). Perhaps this very fact is responsible for fevers neglect as a factor of behavioral determination. Recently, however, Pribor (1956) reported histologically discernable acute neuronal damage from either natural or artificial fever. Such findings suggest that hyperthermia should be investigated for possible chronic effects, including psychological deficit.

“Frustration” from witholding reinforcing intracranial stimulation ☆ ☆☆

Abstract Rats and guinea pigs were trained on a multiple schedule consisting of the following sequence: a fixed ratio of 8:1 which produced a reinforcement and terminated that segment of the schedule; a 10-sec time out; a fixed interval of 2 min which produced a reinforcement and terminated that segment of the schedule; a 10-sec time out; with this cycle recurring regularly in the same sequence. Three reinforcement conditions were used: 20 intracranial self-stimulations (each requiring a separate lever response); 20 intracranial stimulations delivered without the necessity of responding; and sugar water. Frustration consisted of reinforcement being eliminated at the end of an arbitrarily selected fixed-ratio segment, or of extending the time out at the end of such a segment to 2.5 min. For all subjects, responding increased during the fixed-interval segment immediately following frustration. The results supported the hypothesis that intracranial stimulation acts as any conventional reinforcing stimulus.

Effects of Differential Rearing and Levels of Motivation

6 male littermate rats reared from weaning in environments of either reduced or augmented stimulus variety were compared under different conditions of motivational urgency. Tests involving high urgency—initial exposure to an open field, passive (step-down) avoidance of foot-shock, and CER acquisition—showed no differences (ps > .05). The test involving low urgency —extinction of the CER—separated the groups (p < .01).

Heart-rate response during aversive conditioning.

36 rats were used to determine the effects of: (a) footshock before specific training, (b) CS duration (6 vs 60 sec.), and (c) form of aversive conditioning (CER vs CAR) on heart rate both during the presentation of the CS and between presentations. All three tested variables were effective in modifying the heart-rate response to the CS while only CS duration altered heart rates between CS presentations.