Biomedical subjects

N K Dess

Publications and source records attributed to N K Dess.

21 records · Page 2Linked to original sources

PubMed1986

Relative effectiveness of concurrent forward/backward versus simple forward and simple backward Pavlovian conditioning procedures.

Concurrent forward/backward Pavlovian conditioning procedures were compared with simple forward and simple backward procedures for differential excitatory and inhibitory conditioning. Four groups of dogs each received 30 shocks while restrained in a Pavlovian harness. One group of dogs (CON) received concurrent conditioning with a clicker signaling shocks and with a tone following shocks. For another group of dogs (SF), a clicker signaled the shocks, whereas the tone was randomly related to shocks. For a third group (SB), the tone followed shock termination, whereas the clicker was randomly related to shocks. For a fourth group (TRC), both the clicker and the tone were randomly related to shocks. All stimuli were then superimposed on a temporally paced avoidance baseline and their associative properties were assessed relative to the TRC group. Differential excitatory-inhibitory conditioning was significantly reduced in the concurrent procedure relative to that which occurred in the simple conditioning procedures despite exactly equal CS + -US and US-CS-contingencies. These results were interpreted with reference to contextual conditioning effects predicted by the Rescorla-Wagner conditioning model and the theoretical issue of independence vs. interdependence of CS-US associative strengths.

Acoustic Stimulation↗

PubMed1983

Immediate and proactive effects of controllability and predictability on plasma cortisol responses to shocks in dogs.

Controllability and predictability are important modulators of the behavioral effects of aversive stimulation on animals. An experiment was conducted to further investigate both the immediate and proactive effects of controllability and predictability of shocks on adrenocortical responsivity. In an initial stress induction phase, the controllability and predictability of electric shocks were independently varied in groups of dogs, and plasma cortisol responses were measured. In a subsequent test phase, all groups of dogs received identical shocks in a novel situation. Cortisol responses to these test shocks were analyzed as a function of the controllability and predictability of previous induction shocks. The results showed that during stress induction, uncontrollable shocks produced significantly greater cortisol elevations that controllable shocks but that predictability had no significant effect on cortisol responses. However, unpredictable shocks during stress induction acted proactively to significantly increase cortisol response to novel test shocks, whereas prior controllability did not modulate subsequent responsivity to novel shocks.

Animals↗

PubMedDate not supplied

Taste reactivity in rats selectively bred for high vs. low saccharin consumption.

Rats selectively bred for high (HiS) vs. low (LoS) saccharin consumption were compared on taste reactivity responses to 0.1% saccharin before and after continuous access to 0.1% saccharin. The rats were also tested with other saccharin concentrations (0.01-0.3%) before and after the consumption test. Finally, all rats were tested for reactivity to 0.1 M sucrose, 0.0001 M quinine hydrochloride, and a sucrose + quinine mixture. HiS rats ingested more saccharin than did LoS rats, but the groups did not differ in total ingestive or total aversive reactivity on any of the taste tests. When aversive reactivity was analyzed further to distinguish passive drip from other, more active responses, HiS rats made more active responses than LoS rats; the latter showed a consistent tendency to passive drip more than HiS rats. Overall, aversive responding decreased and ingestive responding increased as saccharin concentration rose and from the first to the second concentration series. Because the brain stem-mediated hedonic evaluation of tastes by HiS and LoS rats appears to be similar, the difference in saccharin consumption must be mediated by psychological processes whose neural substrates lie above the brain stem.

Animals↗