Signal functions in discriminated avoidance behavior

Four rats were trained to lever press under a discriminated avoidance/escape schedule in which separately signalled safe and warning periods were 100 sec and 32 sec respectively. The auditory and not the visual component of the compound warning signal became associated with the discriminative control of lever pressing. Avoidance behavior also came under temporal control, in that the probability of lever pressing increased as the warning period progressed. Timing began with the onset of the warning signal rather than the offset of the safe signal. However, after the warning signal had been progressively eliminated, timing began with the offset of the safe signal. When neither signal was normally available, the temporal distribution of avoidance behavior changed markedly. Drifts in the temporal distribution of lever pressing occurred throughout the study; these were manipulated for two animals.     

The role of the cs and avoidance period duration in discriminated avoidance conditioning

In an experiment investigating the effect of CS duration on discriminated bar-press conditioning, subjects were assigned to one warning period duration (1.5, 5.0 or 15.0 sec.) on the first day of avoidance training, and to one of the three durations on the second day of training. On each day avoidance behaviour was greatly influenced by the duration of the CS (warning) period, but the duration on day I had no effect on the second day's avoidance performance. Groups receiving no CS during training, although provided an avoidance contingency, showed little conditioning, but produced highly significant amounts of intertrial responding. In a second experiment, subjects receiving CS on day I were shifted to no CS on day II. Avoidance performance on day II was not significantly different from the day II performance of subjects in Experiment I having two training sessions with the CS present or absent on both days.     

Facilitation of discriminated lever-press avoidance by noncontingent shocks

Two experiments investigated the effect of presenting a brief noncontingent, unsignaled shock prior to warning-signal onset on discriminated lever-press avoidance behavior in rats. The main finding was that noncontingent shock delivered 2 sec but not 16 sec prior to warning-signal onset facilitated avoidance performance and learning. These results were predicted on the basis of shock-elicited response bursting which was expected to increase the operant level of the lever-press response at short shock-warning signal intervals. It was suggested that species-specific limitations on rats' lever-press avoidance are not unconditional, but rather can be overcome with environmental manipulations.     

Hemispheric memory for random forms revisited

Hemispheric short-term memory was studied by projecting complex random forms that varied in their verbal association strength to the left and right hemispheres. Male and female subjects responded same or different to a centrally presented memory test stimulus which occurred 0, 5, 10, or 20 sec after the target item. Reaction time for both response judgments was significantly shorter for right-hemisphere presentations over all memory intervals. For both performance measures, response judgment interacted with the length of memory interval and the verbal association value of the stimulus items. No hemispheric differences were observed as a function of subject sex. Hemispheric memory for complex forms appears primarily dependent upon task processing demands rather than stimulus factors when response time is used to measure recognition under tightly controlled conditions.     

D-Lactate inhibition of memory in a single trial discrimination avoidance task in the young chick

L-Lactate is a metabolite possibly able to meet some neuronal energy demands. However, a clear role for L-lactate in behaviour remains elusive. Administration of the inactive isomer D-lactate (1.75 mM; ic), immediately post-training, resulted in a persistent retention loss from 40 min post-training when used in conjuction with a single trial discrimination avoidance task designed for the young chick. Furthermore, 1mM noradrenaline (ic) administered 20 min post-training overcame the retention loss induced by D-lactate. Although not directly demonstrated in the current study, it is plausible that D-lactate inhibited memory processing by competing with L-lactate for uptake into neurons. The time of onset of the retention loss induced by D-lactate is in accord with findings where the action of noradrenaline is inhibited. The successful challenge of D-lactate inhibition by a high concentration of noradrenaline may suggest a relationship by some unidentified mechanism.     

Two temporal parameters of free operant discriminated avoidance in the rhesus monkey

Four monkeys were exposed to free operant discriminated avoidance (discriminated Sidman avoidance) in a parametric study of safe stimulus and warning stimulus duration. The safe stimulus was assigned values of 2, 5, 10, 20, and 40 sec, the warning stimulus values of 2, 5, and 20 sec. Rate of responding was a decreasing negatively accelerated function of safe stimulus duration, with a small effect attributable to warning stimulus duration. Control of response rate by safe stimulus duration was due to the predominance of responding in the presence of the warning stimulus. Responding during the safe stimulus was independent of the temporal parameters except at schedules combining short safe and short warning stimulus durations. Latencies of responses in the warning stimulus were analyzed, and mean latency was found to be a direct function of warning stimulus duration, with only one exception, resulting from the order in which the warning stimulus values were presented. Shock rate was not systematically related to either of the manipulated parameters.     

A comparison of leverpress and head-poke discriminated Sidman avoidance

A discriminated Sidman avoidance procedure used by Forgione (1970) was replicated using a head-poke response instead of a leverpress as the avoidance operant. The resultant data were described in terms of the five dependent measures reported by Forgione. Head-poke avoidance was found to be more efficient than its leverpress counterpart and compared very favorably with the lever-disabling (or shock-timer-on) procedure used by Forgione to break up inefficient leverpress behavior patterns.     

Hemispheric processing asymmetries: implications for memory

Recent research has demonstrated that memory for words elicits left hemisphere activation, faces right hemisphere activation, and nameable objects bilateral activation. This pattern of results was attributed to dual coding of information, with the left hemisphere employing a verbal code and the right a nonverbal code. Nameable objects can be encoded either verbally or nonverbally and this accounts for their bilateral activation. We investigated this hypothesis in a callosotomy patient. Consistent with dual coding, the left hemisphere was superior to the right in memory for words, whereas the right was superior for faces. Contrary to prediction, performance on nameable pictures was not equivalent in the two hemispheres, but rather resulted in a right hemisphere superiority. In addition, memory for pictures was significantly better than for either words or faces. These findings suggest that the dual code hypothesis is an oversimplification of the processing capabilities of the two hemispheres.     

Exposure to a rhythmic auditory stimulus facilitates memory formation for the passive avoidance task in the day-old chick.

Previous research regarding the beneficial effects of auditory stimuli on learning and memory in humans has been inconsistent. In the current study, day-old chicks were used to reduce the impact of individual differences on responses. Chicks were trained on a passive avoidance task and exposed to various auditory stimuli. Exposure to a complex rhythmic sequence for 1 min strongly facilitated chicks' long-term memory. The optimal time of presentation of the stimulus was between 10 min before and 20 min after training. Moreover, the enhancing effect was not generalized to the other auditory stimuli tested. It is suggested that this effect may be due to arousal because arousal hormones are critical to long-term memory formation. This study indicates that the temporal characteristics and type of stimulus may be important considerations when investigating the effects of auditory stimuli on cognitive functioning.     

Inhibition of monoADP-ribosylation prevents long-term memory consolidation of a single-trial passive avoidance task in the day-old chick

The cytosolic posttranslational protein-modifying mechanism of monoADP-ribosylation has been implicated in long-term potentiation, a synaptic model of memory formation. The current study investigated the effect of inhibiting mono(ADP-ribosyl) transferase on memory for the passive avoidance task in day-old chicks (white Leghorn-black Australorp). Various doses of novobiocin or menadione sodium bisulfite were administered intracranially at different times before or after training. Control chicks were administered saline at matched times. Novobiocin (650 microM) or menadione sodium bisulfite (250 microM) administered between 5.0 min pretraining and 2.5 min posttraining was found to cause a persistent loss of retention from 120 min posttraining. These data provide the first demonstration that monoADP-ribosylation is required for the maintenance of long-term memory. Furthermore, the temporal characteristics of the memory loss caused by monoADP-ribosylation inhibition appears to exclude this mechanism as a downstream effect of the well-established nitric oxide activity previously shown to occur within 40 min of passive avoidance training.     

Hemispheric asymmetries in the time course of recognition memory

Hemispheric specialization has been studied extensively within subfields ranging from perception to language comprehension. However, the study of asymmetries for basic memory functions—an area that holds promise for bridging these low- and high-level cognitive domains—has been sporadic at best. We examined each hemisphere’s tendency to retain verbal information over time, using a continuous recognition memory task with lateralized study items and central test probes. We found that the ubiquitous advantage of the left hemisphere for the processing and retention of verbal information is attenuated and perhaps even reversed over long retention intervals. This result is consistent with theories that propose differences in the degree to which the hemispheres maintain veridical versus semantically transformed representations of the input they receive.     

Gap junctions and memory: An investigation using a single trial discrimination avoidance task for the neonate chick

Gap junctions are important to how the brain functions but are relatively under-investigated with respect to their contribution towards behaviour. In the present study a single trial discrimination avoidance task was used to investigate the effect of the gap junction inhibitor 18-α-glycyrrhetinic acid (αGA) on retention. Past studies within our research group have implied a potential role for gap junctions during the short-term memory (STM) stage which decays by 15 min post-training. A retention function study comparing 10 μM αGA and vehicle given immediately post-training demonstrated a significant main effect for drug with retention loss at all times of test (10–180 min post-training). Given that the most common gap junction in the brain is that forming the astrocytic network it is reasonable to conclude that αGA was acting upon these. To confirm this finding and interpretation two additional investigations were undertaken using endothelin-1 (ET-1) and ET-1 + tolbutamide. Importantly, a retention function study using 10 nM ET-1 replicated the retention loss observed for αGA. In order to confirm that ET-1 was acting on astrocytic gap junctions the amnestic action of ET-1 was effectively challenged with increasing concentrations of tolbutamide. The present findings suggest that astrocytic gap junctions are important for memory processing.     

A scavenger of peroxynitrite prevents long-term memory formation using a single trial passive avoidance task for the day-old chick

The important role of nitric oxide (NO) in memory processing has been recognised for some time. However, the mechanisms through which NO may act are only partially understood. One highly reactive radical brought about by the reaction of NO and superoxide ions is peroxynitrite. The current study investigated the effect of peroxynitrite scavenging on retention for a single trial passive avoidance task developed for the day-old chick. Administration of a range of concentrations of the peroxynitrite scavenger Trolox (0.1 microM-1.2 mM) yielded a bimodal retention curve. This dose-response curve had nadirs at 300 and 800 microM. A time of administration study was conducted for each optimal concentration of Trolox and in both studies, the effective range of administration times extended from at least 10 min before training to 20 min post-training. Finally, a retention function was conducted for each optimum concentration of Trolox and in both studies a persistent retention loss was observed from 40 min post-training until the conclusion of the experiment 24 h post-training. The findings suggest that physiological levels of peroxynitrite may be required for the consolidation of long-term memory in this model of memory formation. Interestingly, the effective times of administration and time of retention loss onset are consistent with previous studies which blocked NO synthesis. Therefore it may be suggested that NO acts to facilitate long-term memory formation through the production of peroxynitrite.