In a previous functional magnetic resonance (fMRI) study, a subdivision of the human auditory cortex into four distinct territories was
achieved. One territory (T1a) exhibited functional specialization in terms of a foreground-background decomposition task involving matching-to-sample monitoring on tone sequences. The present study more specifically determined whether memory-guided analysis of tone sequences is part of the T1a specialization. During the encoding periods, an arbitrary and unfamiliar four-tone-sequence
(melody) played by one instrument was presented. The melody-instrument-combination was different in each period. During subsequent
retrieval periods, learned and additional combinations were presented, and the tasks were either to detect the target melodies
(experiment I) or the target instruments (experiment II). T1a showed larger activation during the melody retrieval. The results
generally suggest that (1) activation of T1a during retrieval is determined less by the sound material than by the executed task, and (2) more
specifically, that memory-guided sequential analysis in T1a is dominant over recognition of characteristic complex sounds.

Birgit Gaschler-Markefski

Frank Baumgart

Claus Tempelmann

Marty G. Woldorff

Henning Scheich

Activation of Human Auditory Cortex in Retrieval Experiments: An fMRI Study

Evidence is growing that the cAMP pathway through the cAMP responsive element binding protein (CREB) transcription factor plays an important role in long-term memory formation (LTM). To study the role of ß-noradrenergic receptors, positively linked to the cAMP secondmessenger system, in the dynamics of LTM processes, we used a memory-reactivation paradigm because recent studies in our laboratory confirmed that reactivated memory is labile and undergoes an extended reconsolidation process. In an eight-arm maze, rats were trained to choose the same three baited arms; 24 hr later, memory was reactivated and then the rats were injected intracerebroventricularly at 5 min, 30 min, 60 min, or 5 hr later with the ß-antagonist timolol or with saline. The results showed that injection of timolol induced amnesia only at the 60 min post-reactivation interval, whereas all control groups and groups that were timolol-injected at other post-reactivation intervals displayed optimal retention. The delayed amnesic action of timoloi suggests that ß noradrenergic receptors and the cAMP cascade are implicated in the late phase of reprocessing of a remembered event.

Pascal Roullet

Susan Sara

Consolidation of Memory After its Reactivation: Involvement of ß Noradrenergic Receptors in the Late Phase

In the young chick, the intermediate medial hyperstriatum ventrale is involved in learning paradigms, including imprinting and passiveavoidance learning. Biochemical changes in the intermediate medial hyperstriatum ventrale following learning include an up-regulation ofamino-acid transmitter levels and receptor activity. To follow the changes of extracellular amino acid levels during passive avoidance training,we used an in vivo microdialysis technique. Probes were implanted in chicks before training the animals, either on a methyl- anthranylate-or water-coated bead. One hour later, recall was tested in both groups by presenting a similar bead. An increase of extra-cellular glutamate levels accompanied training and testing in both groups; during training, glutamate release was higher in methylanthranylate- trained than in water-trained chicks. When compared with the methylanthranylate-trained chicks during testing, the water-trained chicks showed enhanced extra-cellular glutamate levels. No other amino acid examined showed significant changes. After testing, the chicks were anesthetized and release- stimulated with an infusion of 50 mM potassium. Extra-cellular glutamate and taurine levels were significantly increased in both methylanthranylate-and water-trained chicks. The presentation of methylanthranylate as an. olfactory stimulus significantly enhanced glutamate levels, especially in methylanthranylate-trained chicks. The results suggest that such changes in extra-cellularglutamate levels in the intermediate medial hyperstriatum ventrale accompany pecking at either the water- or the methylanthranylate-bead. The taste of the aversant may be responsible for the greater increases found in methylanthranylate-trained birds.

Jonathan N. Daisley

Michael  Gruss

Steven P. R. Rose

Katharina  Braun

Passive Avoidance Training and Recall are Associated With Increased Glutamate Levels in the Intermediate Medial Hyperstriatum Ventrale of the Day-Old Chick

Adrenal steroid hormones modulate learning and memory processes by interacting with specific glucocorticoid receptors at different
brain areas. In this article, certain components of the physiological response to stress elicited by learning situations are proposed to form an
integral aspect of the neurobiological mechanism underlying memory formation. By reviewing the work carried out in different learning models in chicks (passive avoidance learning) and rats (spatial orientation in the Morris water maze and contextual fear conditioning), a role for brain corticosterone action through the glucocorticoid receptor type on the mechanisms of memory consolidation is hypothesized. Evidence is also presented to relate post-training corticosterone levels to the strength of memory storage. Finally, the possible molecular mechanisms that might mediate the influences of glucocorticoids in synaptic plasticity subserving long-term memory formation are considered, mainly by focusing on studies implicating a steroid action through (i) glutamatergic transmission and (ii) cell adhesion molecules.

Carmen Sandi

The Role and Mechanisms of Action of Glucocorticoid Involvement in Memory Storage

Isoforms of apolipoprotein E (ApoE) have been implicated as risk factors in Alzheimer’s disease. We have, therefore, examined the possible role of ApoE in memory formation, using a one-trial passive avoidance task in day-old chicks. Birds were trained on the task and
then at various times pre or post-training were injected intracerebrally with anti-ApoE. Immunofluorescence staining demonstrated the
presence of the antibody bound to the neuropil, close to the injection site and adjacent to the ventricle, with a residence time in the brain of
up to 30 min. Chicks that were injected 30 min pre-training or just post-training with 5μg/ hemisphere of the antibody learned the task, but
were amnesic when tested at 30 min or at subsequent times up to 24 hr Post-training. When tested at 24 hr, birds injected 5.5 hr post-training
showed unimpaired retention. Birds injected with 5μg/hemisphere of anti-ApoA-I (which has a brain distribution similar to that of
anti-ApoE) at 30 min pretraining showed no amnesia, indicating the specificity of the effect to the ApoE. Possible mechanisms for this effect
are discussed.

Chris Lancashire

Radmila Mileusnic

Steven P.R. Rose

Apolipoprotein E Antibodies Affect the Retention of Passive Avoidance Memory in the Chick

Auditory filial imprinting induces quantitative changes of synaptic density in the forebrain area mediorostral neostriatum/hyperstriatum ventrale of the domestic chick. The aim of the present study was to examine the time window and the extent and quality of experience that is required for the induction of these synaptic changes. We found that a brief (30 min) experience with the imprinting situation (tone stimulus + mother surrogate) is sufficient to induce spine elimination, which is detectable
on postnatal day 7, but not 80 min after the presentation of the imprinting stimuli. This synaptic reorganization requires the association of the acoustic imprinting tone with an emotional reward (mother surrogate); acoustic stimulation alone does not lead to detectable synaptic changes. The results of the present study provide further evidence that juvenile emotional learning events, such as filial imprinting, lead to a selective synaptic reorganization.

Jörg Bock

Katharina Braun

Differential Emotional Experience Leads to Pruning of Dendritic Spines in the Forebrain of Domestic Chicks

The role of NMDA and non-NMDA glutamate receptors in long-term potentiation has been intensely investigated, yet recent evidence on the dynamics of synaptic depolarization suggests that the original view should be extended. NMDA receptor-mediated currents, apart from their <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:math> permeability, show a marked voltage dependence, consisting of current increase and slowdown during membrane depolarization. During highfrequency synaptic transmission, NMDA current increase and slowdown are primed by non-NMDA receptor-dependent depolarization and proceed regeneratively. Thus, NMDA receptors make a decisive contribution to membrane depolarization and spike-firing. From the data obtained at the mossy fiber- granule cell synapse of the cerebellum, we propose that the electrogenic role of NMDA receptors is functional to LTP induction. Moreover, during LTP, both NMDA and non- NMDA receptor currents are potentiated, thus establishing a feed-forward mechanism that ultimately enhances spike firing. Thus, NMDA receptors exert an integrated control on signal coding and plasticity. This mechanism may have important implications for information processing at the cerebellar mossy fibergranule cell relay.

Egidio  D&#39;Angelo

Paola  Rossi

Integrated Regulation of Signal Coding and Plasticity by NMDA Receptors at a Central Synapse

Activation of cyclic AMP dependent kinase is believed to mediate slow onset, long-term potentiation (LTP) in central neurons. Cyclic-
AMP activates a cascade of molecular events leading to phosphorylation of the nuclear cAMP responsive element binding protein (pCREB).
Whereas a variety of stimuli lead to activation of CREB, the molecular processes downstream of CREB, which may be relevant to neuronal
plasticity, are yet largely unknown. We have recently found that following exposure to estradiol, pCREB mediates the large increase in dendritic spine density in cultured rat hippocampal neurons. We now extend these observations to include other stimuli, such as
bicuculline, that cause the formation of new dendritic spines. Such stimuli share with estradiol the same mechanism of action in that both require activity-dependent CREB phosphorylation. Our observations suggest that CREB phosphorylation is a necessary, but
perhaps not sufficient, step in the process leading to the generation of new dendritic spines and perhaps to functional plasticity as well.

Menahem Segal

Diane D. Murphy

CREB Activation Mediates Plasticity in Cultured Hippocampal Neurons

About this journal

Neural Plasticity is an interdisciplinary journal dedicated to the publication of articles related to all aspects of neural plasticity, with special emphasis on its functional significance as reflected in behavior and in psychopathology.

Journal profile

Meet the editorial board

Chief Editor, Professor Baudry, is currently University Professor at Western University of Health Sciences in Pomona, CA. His research focuses on understanding the molecular/cellular mechanisms of learning and memory and neurodegeneration.

Editor spotlight

Submit to Special Issue

We currently have a number of Special Issues open for submission. Special Issues highlight emerging areas of research within a field, or provide a venue for a deeper investigation into an existing research area.

Special Issues

Author guidelines

Editorial board

Databases and indexing

Neural Plasticity - Table of contents 1998

title

Neural Plasticity is an interdisciplinary journal dedicated to the publication of articles related to all aspects of neural plasticity, with special emphasis on its functional significance as reflected in behavior and in psychopathology.

Neural Plasticity