TY - JOUR
T1 - Differences in hippocampal neuronal population responses to modifications of an environmental context
T2 - Evidence for distinct, yet complementary, functions of CA3 and CA1 ensembles
AU - Vazdarjanova, Almira
AU - Guzowski, John F.
PY - 2004/7/21
Y1 - 2004/7/21
N2 - Understanding how the hippocampus processes information critical for establishing spatial and declarative memories will benefit greatly from determining not only what kind of information the hippocampus registers, but also how this information is processed across the different hippocampal subfields. We addressed this question using a novel immediate-early gene-based brain-imaging method (Arc/H1a catFISH) that allows comparisons of neuronal ensembles activated by two experiences separated by ∼30 min. Rats exposed to the same environment twice activated CA3 and CA1 ensembles with a similarly high degree of overlap. Changing the identity or configuration of local cues, or changing distal cues, activated CA3 and CA1 ensembles with reduced overlap. Yet, the overlap was greater in CA3 than in CA1. In contrast, rats exposed to two completely different environments activated CA3 and CA1 ensembles with low overlap, and this overlap was even lower in CA3 compared with CA1. Thus, CA3 has a discontinuous, whereas CA1 has a graded, population response to alterations of an environment. Additionally, as indicated by the percentage of active neurons, the context representation was more sparse in CA3 (∼18%) than in CA1 (∼35%). Finally, CA3 and CA1 activity levels were not correlated within a session, arguing against a simple coactivation of these regions. Instead, the within-rat ratio of CA3/CA1 cell activity was correlated across sessions, suggesting that the balance of CA3/CA1 activity is individual specific. Taken together, these findings suggest that CA3 and CA1 neuronal ensembles perform distinct, yet complementary, functions in the processing of spatial and contextual information.
AB - Understanding how the hippocampus processes information critical for establishing spatial and declarative memories will benefit greatly from determining not only what kind of information the hippocampus registers, but also how this information is processed across the different hippocampal subfields. We addressed this question using a novel immediate-early gene-based brain-imaging method (Arc/H1a catFISH) that allows comparisons of neuronal ensembles activated by two experiences separated by ∼30 min. Rats exposed to the same environment twice activated CA3 and CA1 ensembles with a similarly high degree of overlap. Changing the identity or configuration of local cues, or changing distal cues, activated CA3 and CA1 ensembles with reduced overlap. Yet, the overlap was greater in CA3 than in CA1. In contrast, rats exposed to two completely different environments activated CA3 and CA1 ensembles with low overlap, and this overlap was even lower in CA3 compared with CA1. Thus, CA3 has a discontinuous, whereas CA1 has a graded, population response to alterations of an environment. Additionally, as indicated by the percentage of active neurons, the context representation was more sparse in CA3 (∼18%) than in CA1 (∼35%). Finally, CA3 and CA1 activity levels were not correlated within a session, arguing against a simple coactivation of these regions. Instead, the within-rat ratio of CA3/CA1 cell activity was correlated across sessions, suggesting that the balance of CA3/CA1 activity is individual specific. Taken together, these findings suggest that CA3 and CA1 neuronal ensembles perform distinct, yet complementary, functions in the processing of spatial and contextual information.
KW - Arc
KW - Context discrimination
KW - Hippocampus
KW - Homer 1a
KW - Memory
KW - Place cell
UR - http://www.scopus.com/inward/record.url?scp=3242802723&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=3242802723&partnerID=8YFLogxK
U2 - 10.1523/JNEUROSCI.0350-04.2004
DO - 10.1523/JNEUROSCI.0350-04.2004
M3 - Article
C2 - 15269259
AN - SCOPUS:3242802723
SN - 0270-6474
VL - 24
SP - 6489
EP - 6496
JO - Journal of Neuroscience
JF - Journal of Neuroscience
IS - 29
ER -