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Rhythmicity, synchrony and resonance within the circuit of Papez
Title
Rhythmicity, synchrony and resonance within the circuit of Papez.
Creator
Albo Angelus, Zimbul, Florida Atlantic University, Vertes, Robert P.
Abstract/Description
Single unit activity from the anterior thalamus (AT) was recorded in order to investigate discharge profiles during desynchronized (large amplitude irregular activity (LIA)), and synchronized (theta rhythm) patterns of the hippocampal EEG. Units were recorded in urethane-anesthetized rats in the anteroventral (AV, n = 96), the anterodorsal (AD, n = 44) and the anteromedial (AM, n = 48) thalamic nuclei. The majority of the units (n = 164, 87%) were theta-on and a small group (n = 24, 13%) was...
Show moreSingle unit activity from the anterior thalamus (AT) was recorded in order to investigate discharge profiles during desynchronized (large amplitude irregular activity (LIA)), and synchronized (theta rhythm) patterns of the hippocampal EEG. Units were recorded in urethane-anesthetized rats in the anteroventral (AV, n = 96), the anterodorsal (AD, n = 44) and the anteromedial (AM, n = 48) thalamic nuclei. The majority of the units (n = 164, 87%) were theta-on and a small group (n = 24, 13%) was theta-off. Theta-off cells were found in AD and AM nuclei but not in AV. Theta-on cells increased their discharge in presence of hippocampal theta. Mean discharge rate was 6.0 +/- 0.52 Hz and 14.48 +/- 0.96 Hz for AV theta-on cells during control and theta states, 4.43 +/- 0.52 Hz and 10.05 +/- 1.28 Hz for AD theta-on cells, and 2.60 +/- 0.3 Hz and 6.42 +/- 0.9 Hz for AM theta-on cells, respectively. We found that 40% of AV cells showed a rhythmic pattern that peaked significantly at 250--270 ms during theta, 21.9% of AD units and only 5.7% for AM units showed a rhythmic pattern. The majority of AT cells showed unit-theta phase-locked EEG oscillations in the crosscorrelogram, indicating that in spite of low rhythmicity most units firing were modulated at theta frequency. The coherence measured by spectral analysis between unit firing and hippocampal theta was statistically significant in 75% of cases. The anatomical distribution of the cells shows that coherence values were widely distributed across the anterior thalamus. In addition, the particular contribution of this diencephalic structure during theta was determined by applying measures of information flow in the neural circuit of Papez. Partial coherence (PC) analysis together with the computation of causality measures (DTF and DC) was used to study such interaction among AV, retrosplenial cortex and hippocampus. PC analysis revealed hippocampus as the synchronizing structure for rhythmic AV cells and retrosplenial cortex. A link between hippocampus and retrosplenial cortex was found for the non-rhythmic AV group. The DTF analysis showed flow of propagation from AV to hippocampus, hippocampus to retrosplenial cortex and AV to retrosplenial cortex for both groups. The strength of connection changed depending on the state of the animal. Behaviors that have been particularly related to the hippocampal theta activity refer mainly to learning and memory. Activation of large numbers of septo-hippocampal neurons during the generation of the theta rhythm has been proposed as a 'natural tetanizer'. Numerous cellular studies have linked long-term potentiation (LTP) and the hippocampal theta rhythm. The role of theta in memory has been evidenced through lesion studies in animals. Some observations in humans have proposed the anterior thalamus as pivotal for spatial memory. Perhaps the cellular theta activity found in AV plays an important role in the generation and control of the hippocampal theta rhythm and hence in memory and learning.
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Date Issued
2002
PURL
http://purl.flvc.org/fcla/dt/11976
Subject Headings
Neural circuitry, Electroencephalography, Hippocampus (Brain)
Format
Document (PDF)