Roles for the subiculum in spatial information processing, memory, motivation and the temporal control of behaviour

The subiculum is in a pivotal position governing the output of the hippocampal formation. Despite this, it is a rather under-explored and sometimes ignored structure. Here, we discuss recent data indicating that the subiculum participates in a wide range of neurocognitive functions and processes. Some of the functions of subiculum are relatively well-known-these include providing a relatively coarse representation of space and participating in, and supporting certain aspects of, memory (particularly in the dynamic bridging of temporal intervals). The subiculum also participates in a wide variety of other neurocognitive functions too. however. Much less well-known are roles for the subiculum, and particularly the ventral subiculum, in the response to fear, stress and anxiety, and in the generation of motivated behaviour (particularly the behaviour that underlies drug addiction and the response to reward). There is an emerging suggestion that the subiculum participates in the temporal control of behaviour. It is notable that these latter findings have emerged from a consideration of instrumental behaviour using operant techniques; it may well be the case that the use of the watermaze or similar spatial tasks to assess subicular function (on the presumption that its functions are very similar to the hippocampus proper) has obscured rather than revealed neurocognitive functions of subiculum. The anatomy of subiculum suggests it participates in a rather subtle fashion in a very broad range of functions, rather than in a relatively more isolated fashion in a narrower range of functions, as might be the case for

Probing aggressive motivation in a cichlid fish

The duration of startles provides an inverse measure of motivation to resume the previous activity. Here, we use a novel method in which one convict cichlid fish (Amatitlania nigrofasciata) of a competing pair was startled independently of the opponent. Fish were given various opponents and the mean startle duration determined. This mean was negatively correlated with the mean use of highly escalated 'frontal activities' such as biting and frontal display, but not the less escalated lateral displays or tail beating. Thus the startle duration was a reliable surrogate measure of the most escalated components of aggressive interactions. That is, it provided a motivational probe for aggressiveness of individual fish. Fight motivation is often determined in terms of fight duration or physiological costs for losers, who reveal the costs they are prepared to pay. We discuss various potential advantages of the motivational probe over previous measures, particularly with respect to winners and losers and different times during the interactions.

Pain experience in hermit crabs?

Pain may be inferred when the responses to a noxious stimulus are not reflexive but are traded off against other motivational requirements, the experience is remembered and the situation is avoided in the future. To investigate whether decapods feel pain we gave hermit crabs, Pagurus bernhardus, small electric shocks within their shells. Only crabs given shocks evacuated their shells indicating the aversive nature of the stimulus, but fewer crabs evacuated from a preferred species of shell indicating a motivational trade-off. Some crabs that evacuated attacked the shell in the manner seen in a shell fight. Most crabs, however, did not evacuate at the stimulus level we used, but when these were subsequently offered a new shell, shocked crabs were more likely to approach and enter the new shell. Furthermore, they approached that shell more quickly, investigated it for a shorter time and used fewer cheliped probes within the aperture prior to moving in. Thus the experience of the shock altered future behaviour in a manner consistent with a marked shift in motivation to get a new shell to replace the one occupied. The results are consistent with the idea of pain in these animals. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Motivation matters: cheliped extension displays in the hermit crab, Pagurus bernhardus, are honest signals of hunger

Whether animal signals convey honest information is a central evolutionary question, since selection pressures could, in some circumstances, favour dishonesty. A prior study of signalling in hermit crabs proposed that the cheliped extension display of Pagurus bernhardus might represent such an instance of dishonesty. A limitation of this conclusion, however, was that honesty was defined in the context of size assessment, neglecting the potential information that displays might transmit about signallers' variable internal states. Recent analyses of signalling in this same species have shown that its displays provide reliable information about the amount of risk crabs are prepared to tolerate, which therefore might enable signallers to use these displays to honestly convey their motivation to take such risks. Here we test this 'honest advertisement of motivation' hypothesis by varying crabs' need for food and analysing their signalling during simulated feeding conflicts against a model. When crabs were starved for 1-5 days, they dropped significantly in weight. Despite this decrement in resource-holding potential and energy reserves, crabs were more likely to perform cheliped extension displays the longer they were food deprived. Longer-starved crabs, whose subjective resource value was greater, also displayed at a higher rate and were more likely to risk seizing the food from the model. We conclude that cheliped extension is a reliable indicator of crabs' internal state and suggest how this honest signal might operate in conflicts over a variety of other resources in addition to food. We propose that future studies detecting apparent dishonesty should analyse many possible signal-state correlations before concluding a signal is actually dishonest. (c) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.