Contrasting hippocampal and perirhinal cortex function using immediate early gene imaging.

The perirhinal cortex and hippocampus have close anatomical links, and it might, therefore, be predicted that they have close, interlinked roles in memory. Lesion studies have, however, often failed to support this prediction, providing dissociations and double dissociations between the two regions on tests of object recognition and spatial memory. In a series of rat studies we have compared these two regions using the expression of the immediate early gene c-fos as a marker of neuronal activity. This gene imaging approach makes it possible to assess the relative involvement of different brain regions and avoids many of the limitations of the lesion approach. A very consistent pattern of results was found as the various hippocampal subfields but not the perirhinal cortex show increased c-fos activity following tests of spatial learning. In contrast, the perirhinal cortex but none of the hippocampal subfields show increased c-fos activity when presented with novel rather than familiar visual objects. When novel scenes are created by the spatial rearrangement of familiar objects it is the hippocampus and not the perirhinal cortex that shows c-fos changes. This double dissociation for gene expression accords with that found from lesion studies and highlights the different contributions of the perirhinal cortex and hippocampus to memory.     

On immediate function

Behavior is a property of living organisms, not of inanimate matter. The problems of physical science are to understand how a phenomenon works; biological science adds the questions of what a phenomenon does and how something that does such things came to be. Exclusive dedication to cause–effect explanations ignores how behavior helps creatures cope with their internal and external environments. Laws of causation describe the precursors to behavior; laws of function describe the effects of behavior. The numerous instances of learning reflect the many ways that selective pressure for altering behavior on the basis of experience has been manifested. Little basis exists for assuming that the various forms of learning reflect either common functions or common processes. Instead, it seems that evolutionary processes have resulted in domain-specific learning. The rules of learning must be understood in terms of the function that the particular manifestation of learning serves for the organism. Evolutionary theory provides the framework for understanding function as well as relations between function and causal mechanisms.     

The immediate and sustained effects of acute exercise on planning aspect of executive function

ObjectiveThe purpose of this study was to clarify the immediate and sustained effects of an acute bout of exercise on the planning aspects of executive function.DesignThis study used a 2 × 4 true experimental design.MethodForty participants were randomly assigned to either the exercise or control groups and completed the Tower of London task prior to, immediately following, 30 min after, and 60 min after cessation of a 30 min, moderate intensity cycling exercise.ResultsAcute exercise positively impacted the total move score, which reflects planning efficiency, immediately after the cessation of exercise. Acute exercise also led to longer total initiation times, which were linked to better response inhibition of planning at 30 and 60 min after the cessation of exercise.ConclusionAcute exercise benefits planning, and the types of planning and the time points at which they were assessed modulate the relationship between acute exercise and executive function. Exercise-induced physiological and biological fluctuations have been proposed to explain the effects present immediately after exercise, and the mechanisms of such effects warrant further exploration.     

Conjunctive representations in learning and memory: principles of cortical and hippocampal function

The authors present a theoretical framework for understanding the roles of the hippocampus and neocortex in learning and memory. This framework incorporates a theme found in many theories of hippocampal function: that the hippocampus is responsible for developing conjunctive representations binding together stimulus elements into a unitary representation that can later be recalled from partial input cues. This idea is contradicted by the fact that hippocampally lesioned rats can learn nonlinear discrimination problems that require conjunctive representations. The authors' framework accommodates this finding by establishing a principled division of labor, where the cortex is responsible for slow learning that integrates over multiple experiences to extract generalities whereas the hippocampus performs rapid learning of the arbitrary contents of individual experiences. This framework suggests that tasks involving rapid, incidental conjunctive learning are better tests of hippocampal function. The authors implement this framework in a computational neural network model and show that it can account for a wide range of data in animal learning.     

Contrasting reduced overshadowing and blocking

Preexposure of a cue without an outcome (X-) prior to compound pairings with the outcome (XZ-->O) can reduce overshadowing of a target cue (Z). Moreover, pairing a cue with an outcome (X-->O) before compound training can enhance its ability to compete with another cue (i.e., blocking). Four experiments were conducted in a conditioned bar-press suppression preparation with rats to determine whether spacing of the X- or X-->O trials would differentially affect reduced overshadowing and blocking. Experiment 1a showed that reduced overshadowing was larger with massed trials than with spaced trials. Experiment 1b found that blocking was larger with spaced trials than with massed trials. Experiments 2a and 2b indicated that these effects of trial spacing were both mediated by the associative status of the context at test. The results are interpreted in the framework of contemporary learning theories.     

Contrasting Grammatical and Lexical Determiners

This paper investigates the difference between the production of grammatical determiners and lexical determiners in the production of adjective-noun phrases (NPs) in Danish. Models of sentence processing (Garrett in Psychology of learning and motivation, Academic press, New York, pp 133–177, 1975; Bock in J Mem Lang 26(2):119–137, 1987) suggest that the phonological encoding stage of grammatical items can only be specified once lexical items have been phonologically encoded. In their usage-based linguistic theory of the grammar-lexicon distinction, Boye and Harder (Lang 88(1):1–44, 2012) propose that this later encoding of grammatical elements is motivated by two specific features of grammatical elements. The first feature, dependence, is that grammatical items (morphemes, words, constructions) cannot be produced in isolation, but are always dependent on a lexical host item. This feature entails a more complex processing which might lead to longer reaction times when comparing the production of NPs with a grammatical determiner to a lexical one. Additionally, a more complex processing might lead to a lower accuracy rate for the grammatical condition relative to the lexical one. The second feature, low prominence, is that grammatical items code background information and therefore cannot convey the main point of a linguistic message. Less focus on grammatical elements might lead to a lower accuracy rate for the production of grammatical elements relative to lexical ones. Those predictions were tested in a task comparing the production of Danish grammatical determiners (indefinite articles) with the production of lexical ones (numerals, which are homonymous with the articles except for a stress difference) in similar contexts. Group-based analyses were performed in order to take inter-individual differences into account. The results show that the two features as proposed by Boye and Harder (2012) are only revealed for the fastest speakers group but not the slower ones.     

Dynamic shifts in corticostriatal expression patterns of the immediate early genes Homer 1a and Zif268 during early and late phases of instrumental training

Adaptive motor actions require prior knowledge of instrumental contingencies. With practice, these actions can become highly automatic in nature. However, the molecular and anatomical substrates mediating these related forms of learning are not understood. In the present study, we used in situ hybridization to measure the mRNA levels of two immediate early genes (IEGs) in an instrumental paradigm where rats learned to lever-press for food. We report that after three training sessions, Homer 1a and Zif268 (an effector and regulatory IEG, respectively) were significantly induced within an extensive corticostriatal network relative to untrained controls. With extended training (23 sessions), however, a shift in the expression patterns of the two genes was evident. Expression of Homer 1a (official symbol Homer1) decreased significantly in frontal and cingulate cortices, whereas striatal expression was generally maintained. Interestingly, Homer 1a expression markedly increased with extensive training in the ventrolateral region of the striatum (VLS) relative to early learners, suggesting that plasticity in the VLS is required for the efficient production of the learned behavior or in habit formation. Zif268 (official symbol Egr1) expression generally decreased with extensive training; however, these changes were not significant. These results demonstrate for the first time, on a molecular level, a dynamic shift in the contribution of corticostriatal systems mediating the early acquisition and consolidation of goal-directed responses to those engaged after extensive training.     

Unpacking the cognitive map: the parallel map theory of hippocampal function

In the parallel map theory, the hippocampus encodes space with 2 mapping systems. The bearing map is constructed primarily in the dentate gyrus from directional cues such as stimulus gradients. The sketch map is constructed within the hippocampus proper from positional cues. The integrated map emerges when data from the bearing and sketch maps are combined. Because the component maps work in parallel, the impairment of one can reveal residual learning by the other. Such parallel function may explain paradoxes of spatial learning, such as learning after partial hippocampal lesions, taxonomic and sex differences in spatial learning, and the function of hippocampal neurogenesis. By integrating evidence from physiology to phylogeny, the parallel map theory offers a unified explanation for hippocampal function.     

Form and function in early communication: language and pointing gestures

Pointing gestures of verbally advanced 2-year-olds were contrasted with those of less advanced peers, in order to examine the relationships of gesture to language during the acquisition of each. Hypotheses regarding the replacement of gestural functions by speech as verbal skills improve, regarding developmental correspondences between the two communicative domains, and regarding the independence of language acquisition from nonverbal developments were drawn from evolutionary, structuralist, and nativist viewpoints, respectively. Both formal and functional aspects of each communicative skill were measured, and were shown to be largely unrelated, particularly in the gestural domain. No evidence that language replaced gesture for communication in ontogeny was obtained. Correspondences between gesture and language occurred only between functional aspects of each, and the independence of developing language from gestural advances was suggested by the findings.     

Differential interaction of platelet-activating factor and NMDA receptor function in hippocampal and dorsal striatal memory processes

The interaction between platelet activating factor (PAF) and NMDA receptor function in hippocampal and dorsal striatal memory processes was examined. In both a hidden and a visible platform water maze task, peripheral post-training injection of MK-801 (0.05 mg/kg) impaired memory. Post-training intrahippocampal infusions of PAF (1.0 microg/0.5 microl) enhanced memory in the hidden platform task, while intradorsal striatal infusion of PAF (1.0 microg/0.5 microl) enhanced memory in the visible platform task. The memory impairing effects of post-training injection of MK-801 was blocked by concurrent intrahippocampal infusion of PAF. In contrast, post-training injection of MK-801 blocked the memory enhancing effects of concurrent intradorsal striatal infusion of PAF. The results suggest that (1) the memory enhancing effects of intracerebral PAF infusion involve an interaction with NMDA receptor function, and (2) the nature of this interaction may represent a differential mechanism mediating the distinct roles of the hippocampus and dorsal striatum in cognitive memory and stimulus-response habit formation, respectively.     

Binocular rivalry and immediate memory

Three experiments examine features of a simple memory task on which right-handed, right eye dominant subjects have been reported to recall digits projected to the right eye more accurately than those projected simultaneously to the left eye. Superior recall by these subjects of information projected to the right eye was observed only when stimuli projected simultaneously to both eyes were seen as overlapped in the binocular percept. Under monocular presentations, accurracy of recall was not related to the eye with which stimuli were viewed. The binocular oveslap condition has a significance other than that of simply increasing the difficulty of identifying the elements in a visual display for there were no differences in accuracy of recall from each eye when overlapped stimuli were viewed monocularly. More accurate recall of right eye information appears to reflect the resolution of a conflict between inputs from each eye. The possible relation of this finding to cerebral dominance is also discussed. Order of recall in these experiments depended mainly on spatial cues provided by the experimental situation.