Modern views on learning and memory accept the notion of biological constraints--that the formation of association is not uniform across all stimuli. Yet cellular evidence of the encoding of selective associations is lacking. Here, conditioned stimuli (CSs) and unconditioned stimuli (USs) commonly employed in two basic associative learning…

Relating storage of specific information to a particular neuromorphological change is difficult because behavioral performance factors are not readily disambiguated from underlying cognitive processes. This issue is addressed here by demonstrating robust reorganization of the hippocampal mossy fiber terminal field (MFTF) when adult rats learn the…

Dishabituation has been thought to be due either to reversal of the process of habituation or to a second process equivalent to sensitization superimposed on habituation. One way to address this question is by testing whether dishabituation and sensitization can be dissociated. Previous studies using this approach in "Aplysia" have come to…

Psychostimulant exposure has been shown to cause molecular and cellular changes in prefrontal cortex. It has been hypothesized that these drug-induced changes might affect the operation of prefrontal-limbic circuits, disrupting their normal role in controlling behavior and thereby leading to compulsive drug-seeking. To test this hypothesis, we…

The regulated trafficking of GluR1 contributes significantly to synaptic plasticity, but studies addressing the function of the GluR1 C-terminal PDZ-ligand domain in this process have produced conflicting results. Here, we resolve this conflict by showing that apparently similar C-terminal mutations of the GluR1 PDZ-ligand domain result in…

While there is evidence that feedback projections from cortical and neuromodulatory structures to the olfactory bulb are crucial for maintaining the oscillatory dynamics of olfactory bulb processing, it is not clear how changes in dynamics are related to odor perception. Using electrical lesions of the olfactory peduncle, sparing output from the…

Previous studies showed that the serum- and glucocorticoid-inducible kinase ("sgk") gene plays an important role in long-term memory formation. The present study further examined the role of SGK in long-term potentiation (LTP). The dominant-negative mutant of "sgk," SGKS422A, was used to inactivate SGK. Results revealed a time-dependent increase…

In two H[subscript 2] [superscript 15]O PET scan experiments, we investigated the cerebral correlates of explicit and implicit knowledge in a serial reaction time (SRT) task. To do so, we used a novel application of the Process Dissociation Procedure, a behavioral paradigm that makes it possible to separately assess conscious and unconscious…

The ability to learn and retain novel information depends on a system of structures in the medial temporal lobe (MTL) including the hippocampus and the surrounding entorhinal, perirhinal, and parahippocampal cortices. Damage to these structures produces profound memory deficits; however, the unique contribution to memory of each of these…

We have used a genetically tractable model system, the fruit fly "Drosophila melanogaster" to study the interdependence between sensory processing and associative processing on learning performance. We investigated the influence of variations in the physical and predictive properties of color stimuli in several different operant-conditioning…

The prefrontal cortex is involved in the integration and interpretation of information for directing thoughts and planning action. Working memory is defined as the active maintenance of information in mind and is thought to lie at the core of many prefrontal functions. Although dopamine and other neurotransmitters have been implicated, the…

Recent evidence indicates that certain forms of memory, upon recall, may return to a labile state requiring the synthesis of new proteins in order to preserve or reconsolidate the original memory trace. While the initial consolidation of "instrumental memories" has been shown to require de novo protein synthesis in the nucleus accumbens, it is not…

Permanent lesions in the medial prefrontal cortex (mPFC) affect acquisition of conditioned responses (CRs) during trace eyeblink conditioning and retention of remotely acquired CRs. To clarify further roles of the mPFC in this type of learning, we investigated the participation of the mPFC in mnemonic processes both during and after daily…

Learning to associate a conditioned (CS) and unconditioned stimulus (US) results in changes in the processing of CS information. Here, we address directly the question whether chemical appetitive conditioning of "Lymnaea" feeding behavior involves changes in the peripheral and/or central processing of the CS by using extracellular recording…

Many studies of the neural mechanisms of learning have focused on habituation, a simple form of learning in which a response decrements with repeated stimulation. In the siphon-elicited siphon withdrawal reflex (S-SWR) of the marine mollusk "Aplysia," the prevailing view is that homosynaptic depression of primary sensory afferents underlies…