The effect of US signalling and the US-CS interval on backward conditioning in mice.

The effect of US signalling and the US-CS interval in backward conditioning was assessed in mice. For one group of mice the presentation of food was signalled by a tone and for another group, food was unsignalled. For half of the mice, within each group, the presentation of food preceded a visual cue by 10 s. For the other half, food was presented at the start of the visual cue (0-s US-CS interval), resulting in simultaneous pairings of these events. A summation test and a subsequent retardation test were used to assess the inhibitory effects of backward conditioning in comparison to training with a non-reinforced visual cue that controlled for the possible effects of latent inhibition and conditioned inhibition caused as a consequence of differential conditioning. In the summation test unsignalled presentations of the US resulted in inhibition when the US-CS interval was 10 s, but not 0 s. Signalled presentations of the US resulted in inhibition, independent of the US-CS interval. In the retardation test, independent of US signalling, a US-CS interval of 10 s failed to result in inhibition, but an interval of 0 s resulted in greater conditioned responding to the backward CS than the control CS. A generalisation decrement account of the effect of signalling the US with a 0-s US-CS interval, which resulted in reduced responding in the summation test and faster acquisition in the retardation test, is discussed.

Dissociable effects of surprise and model update in parietal and anterior cingulate cortex.

Brains use predictive models to facilitate the processing of expected stimuli or planned actions. Under a predictive model, surprising (low probability) stimuli or actions necessitate the immediate reallocation of processing resources, but they can also signal the need to update the underlying predictive model to reflect changes in the environment. Surprise and updating are often correlated in experimental paradigms but are, in fact, distinct constructs that can be formally defined as the Shannon information (IS) and Kullback-Leibler divergence (DKL) associated with an observation. In a saccadic planning task, we observed that distinct behaviors and brain regions are associated with surprise/IS and updating/DKL. Although surprise/IS was associated with behavioral reprogramming as indexed by slower reaction times, as well as with activity in the posterior parietal cortex [human lateral intraparietal area (LIP)], the anterior cingulate cortex (ACC) was specifically activated during updating of the predictive model (DKL). A second saccade-sensitive region in the inferior posterior parietal cortex (human 7a), which has connections to both LIP and ACC, was activated by surprise and modulated by updating. Pupillometry revealed a further dissociation between surprise and updating with an early positive effect of surprise and late negative effect of updating on pupil area. These results give a computational account of the roles of the ACC and two parietal saccade regions, LIP and 7a, by which their involvement in diverse tasks can be understood mechanistically. The dissociation of functional roles between regions within the reorienting/reprogramming network may also inform models of neurological phenomena, such as extinction and Balint syndrome, and neglect.

Changes in attention to relevant and irrelevant stimuli during spatial learning.

Rats were trained in 2 experiments to find a submerged platform that was situated in 1 of 2 of the 4 corners of a rectangular pool with a curved long wall. Different landmarks occupied 2 of the corners on every trial, and the platform was always situated near a landmark. For the place group in each experiment, the location of the platform was indicated by the shape of the pool and stimuli outside the pool (place cues), but not the landmarks within the pool. For the landmark groups, the landmarks, not the place cues, indicated where the platform could be found. During Stage 2, 2 of the place cues were relevant, and 2 of the landmarks were irrelevant, for a new discrimination. The place cues better controlled searching for the platform in the place group than in the landmark group when the place cues had initially been relevant by signaling the presence (Experiment 1) or the absence (Experiment 2) of the platform. The results show that animals pay more attention to relevant than irrelevant cues.

Latent spatial learning in an environment with a distinctive shape.

Four experiments were conducted with rats in order to determine whether being placed on a platform in one corner of a rectangular swimming pool results in latent spatial learning. Rats in Experiments 1-3 received four trials a day of being placed on the platform. During a subsequent test trial, in which they were released into the pool without the platform, the rats exhibited a preference for swimming in the correct corners of the pool (those with the same geometric properties as the corner containing the platform during training), than the two remaining, incorrect corners. This effect was seen when the interval between the final placement trial and the test trial was as much as 24 hr (Experiment 2) and after varying numbers of sessions of placement training (Experiment 3). Experiment 4 revealed that when the test took place in a kite-shaped arena, after placement training in a rectangle, a stronger preference was shown for the corner that was geometrically equivalent to the correct rather than the incorrect corners in the rectangle. The placement treatment is said to result in latent spatial learning based on the development of S-S associations.