Excitotoxic lesions of the perirhinal cortex leave intact rats' gustatory sensory preconditioning.

We report findings from two sensory preconditioning experiments in which rats consumed two flavoured solutions, each with two gustatory components (AX and BY), composed of sweet, bitter, salt, and acid elements. After this pre-exposure, rats were conditioned to X by pairing with lithium chloride. Standard sensory preconditioning was observed: Consumption of flavour A was less than that of B. We found that sensory preconditioning was maintained when X was added to A and B. Both experiments included one group of rats with lesions of the perirhinal cortex, which did not influence sensory preconditioning. We discuss our findings in the light of other sensory preconditioning procedures that involve the perirhinal cortex and conclude that differences in experimental variables invoke different mechanisms of sensory preconditioning, which vary in their requirement of the perirhinal cortex.

Resilient allocentric reorientation following transfer from the inside to the outside of an arena.

In two virtual spatial-navigation experiments, participants were trained to find a hidden goal that was located adjacent to one of the right-angled corners of a cross-shaped virtual environment. The location of the goal was defined solely with respect to the geometry of the environmental structure. Training trials started from a single central start location (Experiment 1) or from multiple start locations over 2, 4, or 16 training trials (Experiment 2). Following training, participants were placed onto the outside of the same environment and asked to again find the hidden goal (which, unbeknown to participants, was removed) during a single test trial. The results from both experiments revealed that participants spent more time searching in regions on the outside of the environment that were closest to the location where the hidden goal was positioned during the previous training stage. In contrast, participants spent very little time searching in regions whose visual appearance matched those regions that contained the hidden goal during training. These results reproduce the findings from previous research which supports the idea of an allocentric encoding of the shape of the environment during navigation and further implies that this encoding is relatively resilient to manipulations that might be expected to undermine it.

Web-based indicated prevention of common mental disorders in university students in four European countries - Study protocol for a randomised controlled trial.

BACKGROUND: Mental disorders and their symptoms are highly prevalent in the university student population, and the transition from secondary to tertiary education is associated with a rise in mental health problems. Existing web-based interventions for the prevention of common mental disorders in student populations often focus on just one disorder and have not been designed specifically for students. There is thus a need for transdiagnostic, student-specific preventative interventions that can be widely disseminated. This two-arm, parallel group randomised controlled trial aims to evaluate the effectiveness and cost-effectiveness of a web-based transdiagnostic mental health problem prevention programme (PLUS) across several universities in four countries. METHOD: Students (N = 5550) will be recruited through a variety of channels and asked to complete a personality assessment to determine whether they are at high risk for developing common mental disorders. Students at high risk will be randomly allocated to either PLUS or a control intervention, which provides practical support around issues commonly experienced at university. Students at low risk will be allocated to the control intervention. Both intervention groups will be assessed at baseline, 4 weeks, 3 months, 6 months and 12 months after randomisation. Depression and generalised anxiety, assessed using the Patient Health Questionnaire and the Generalised Anxiety Disorder scales, will form the primary outcomes in this study. Secondary outcome measures include alcohol and drug use, eating behaviour, self-esteem, and quality of life. The cost-effectiveness of the intervention will also be evaluated. CONCLUSIONS: This study will contribute to understanding the role of transdiagnostic indicated web-based interventions for the prevention of common mental disorders in university students. It will also be one of the first studies to investigate the cost-effectiveness of such interventions. TRIAL REGISTRATION: This trial was registered in the ISRCTN register (ISRCTN15570935) on 12th February 2016.

Familiarity-based stimulus generalization of conditioned suppression.

We report that stimulus novelty/familiarity is able to modulate stimulus generalization and discuss the theoretical implications of novelty/familiarity coding. Rats in Skinner boxes received clicker → shock pairings before generalization testing to a tone. Before clicker training, different groups of rats received preexposure treatments designed to systematically modulate the clicker and the tone's novelty and familiarity. Rats whose preexposure matched novelty/familiarity (i.e., either both or neither clicker and tone were preexposed) showed enhanced suppression to the tone relative to rats whose preexposure mixed novelty/familiarity (i.e., only clicker or tone was preexposed). This was not the result of sensory preconditioning to clicker and tone. (PsycINFO Database Record

Improved spontaneous object recognition following spaced preexposure trials: evidence for an associative account of recognition memory.

Rodents' biased exploration of a novel object over a familiar object is taken as an indication of recognition memory. According to a general associative model of memory, the biased exploration is a consequence of reduced processing of the familiar object. A component of the reduction of stimulus processing is the result of the operation of Arena → Object associations that are best formed during widely spaced presentations of the stimulus. Results of extant experiments support this prediction but so, too, do accounts based on the effects of handling cues. We report an experiment in which handling cues are matched across stimulus-spacing treatments but that retain improved recognition memory with widely spaced stimulus presentation.

Excitotoxic perirhinal cortex lesions leave stimulus-specific habituation of suppression to lights intact.

Previous experiments demonstrate a normal decline in unconditioned responding in rats with perirhinal cortex lesions but attenuated performance on spontaneous object recognition (SOR), a finding supporting the assertion that distinct systems support these phenomena. This finding informs on the nature of these two fundamental forms of learning and may be taken as support for certain contemporary theories of memory. However, we cannot quantify the relative contributions of genuine habituation and alternative, trivial sources in response decline from effector fatigue and sensory adaptation in these demonstrations. An important implication of this problem is that previous reports may have missed perirhinal-dependent habituation. We report perirhinal cortex lesions to be without effect in rats' habituation of suppression to lights when any influence of effector fatigue and sensory adaptation is eliminated. Theoretical implications of this finding are discussed.

Indirect object recognition: evidence for associative processes in recognition memory.

Rats' exploration of stimulus P (e.g., a domestic object) is reduced following either its direct exposure or its indirect exposure and is taken to indicate recognition memory. Procedures for demonstrating indirect object recognition involve an initial presentation of object P with stimulus X (and of an object Q with stimulus Y). On test, stimulus X is presented with objects P and Q and rats' exploration of Q exceeds their exploration of P. One interpretation here is that the presentation of stimulus X on test associatively activates the memory of object P, which diminishes exploration of P relative to Q. It is possible, instead, that performance is simply the result of a novel pattern of stimulation generated by the unfamiliar combination of X and Q. The authors modified this procedure to reduce the likelihood of such a process. Their procedure involved first the presentation of PX and QY before the presentation of stimulus X alone. During the test that followed, objects P and Q were presented but stimulus X was removed. The authors found that exploration of Q remained greater than that of P despite these modifications and discuss some theoretical implications of indirect, associative processes in recognition memory.

Familiarity-based stimulus generalization of conditioned suppression in rats is dependent on the perirhinal cortex.

We report that bilateral, excitoxic lesions of the perirhinal cortex attenuate rats' familiarity-based stimulus generalization. After surgery, rats were preexposed either to 2 auditory stimuli (A and B) or to only 1 auditory stimulus (B). Following preexposure, all rats received pairings of A and a footshock before assessment of generalized responding (conditioned suppression) to B. Sham rats' generalization was greater when preexposure was to both A and B than when preexposure was to B only. That pattern was abolished in lesioned rats, though no general deficiency was found in other measures of auditory processing. Our findings suggest that the perirhinal cortex is required for rats to encode familiarity as part of stimulus representations.

Domestic cats (Felis catus) do not show causal understanding in a string-pulling task.

This study explored how domestic cats perform in a horizontal string-pulling task to determine whether they understand this case of physical causality. Fifteen cats were tested on their ability to retrieve an unreachable food treat in three different set-ups: (a) a single baited string, (b) two parallel strings where only one was baited and (c) two crossed strings where only one was baited. All cats succeeded at pulling a single string to obtain a treat, but none consistently chose the correct string when two strings were parallel. When tested with two crossed strings one cat chose the wrong string consistently and all others performed at chance level. There was no evidence that cats understand the function of the strings or their physical causality.