SLEEP 2011 Abstract Supplement

A. Basic Science IV. Neurobiology
in the sensorimotor network. However, in DMN, the only significant
decreased connectivity is found between PCC and medial prefrontal
cortex from stage two to SWS. In contrast, REM sleep reactivates the
functional connectivity in both networks as regarded as in the awake
condition. Comparing the post-sleep resting scans with pre-sleep, the
dissociations are observed in sensorimotor network when wake-up, but
spatial reconsolidation in DMN appears to be an after-sleep effect.
Conclusion: Significant reduction of functional connectivity was found
in both networks during sleep, which may be associated with the fading
consciousness in sleep. The breakdown of functional connectivity may
be a common feature representing the rejuvenation effect of sleep. Reconsolidation
of DMN and remained dissociation of sensorimotor network
might indicate the full recovery of self-consciousness but ongoing
integrity of disrupted somato-sensations. Such phenomenon merit future
investigations for discovering brain functions during sleep.
Support (If Any): Intramural Research Program of the National Institute
on Drug Abuse (NIDA) and National Science Council, Taiwan(NSC98-
2917-I-564-158)
0104
INTERACTIONS BETWEEN CORE AND MATRIX
THALAMOCORTICAL PROJECTIONS IN HUMAN SLEEP
SPINDLE SYNCHRONIZATION
Bonjean M 1,2 , Baker T 1 , Cash S 3 , Bazhenov M 4 , Halgren E 5 , Sejnowski
T 1,2
1
Howard Hughes Medical Institute, The Salk Institute for
Biological Studies, La Jolla, CA, USA, 2 Department of Biomedical
Sciences, University of California, San Diego, La Jolla, CA, USA,
3
Massachussets General Hospital, Harvard Medical School, Boston,
MA, USA, 4 Department of Cellular Biology and Neuroscience,
University of California, Riverside, Riverside, CA, USA, 5 Department
of Neurosciences, University of California, San Diego, La Jolla, CA,
USA
Introduction: Human sleep spindles are highly synchronous across the
scalp when measured with EEG channels, but not when measured simultaneously
with MEG sensors which exhibit low correlation and low
coherence with each other and with EEG signals. In this study, we used a
computational model to explore the hypothesis that interactions between
the core and matrix thalamocortical subsystems were responsible for the
complex spatiotemporal patterns of spindle synchronization observed
experimentally.
Methods: To adequately investigate our hypothesis in light of the human
experimental data mentioned above, we constructed a realistic
four-layer model of the thalamus and the cortex, comprising two main
distinct but interconnected thalamocortical pathways known from the
primate literature: (i) core pathway, which has thalamic afferents in the
middle layers of the cortex, mostly layers III and IV, and (ii) matrix
pathway, which has thalamic afferents to superficial layers of the cortex,
mostly layer I.
Results: We found that the relative synchrony of spindle oscillations
between core and matrix networks depends on the pattern of intracortical
connections between the networks. Increasing the fanout of thalamocortical
connectivity in the matrix system while keeping it constant
in the core system led to increased synchrony of the spindle activity in
the matrix system. In constrast, increasing the cortico-thalamic fanout or
cortico-cortical connectivity between matrix and core systems had no effect
on spindle synchrony. Conversely, the latency for spindles to spread
from the core to matrix subsystem was independent of thalamocortical
fanout, but highly dependent on the probability of connections between
the systems.
Conclusion: Our results suggests that the known anatomical differences
between matrix and core subsystems in thalamocortical fanout
may be necessary and sufficient to produce different levels of synchrony
of spindle discharges between different cortical locations. These differ-
ences may explain the discrepancies between spindles simultaneously
recorded by EEG versus MEG.
Support (If Any): This study was supported by NIH-NIBIB (Grant
1R01EB009282-01).
0105
CORTICOTHALAMIC FEEDBACK CONTROLS SLEEP
SPINDLE DURATION IN VIVO
Bonjean M 1,2 , Baker T 1 , Lemieux M 3 , Timofeev I 3 , Sejnowski T 1,2 ,
Bazhenov M 4
1
Howard Hughes Medical Institute, The Salk Institute for Biological
Studies, La Jolla, CA, USA, 2 Department of Biomedical Sciences,
University of California, San Diego, La Jolla, CA, USA, 3 School
of Medicine, Laval University, Quebec, QC, Canada, 4 Department
of Cellular Biology and Neuroscience, University of California,
Riverside, Riverside, CA, USA
Introduction: Evidence from slice experiments and modeling studies
has supported a mechanism for spindle termination mediated by upregulation
of the hyperpolarization activated depolarizing current (Ih), which
is dependent on intracellular Ca2+ concentration. In the present study
using a combination of in vivo and modeling experiments, we provide,
for the first time, compelling evidence that the cortical feedback plays
an active role in terminating spindle oscillations by desynchronizing
thalamocortical neurons, effectively controlling the duration of spindles.
Methods: Electrophysiological experiments were conducted in cats
(n=5) under general anesthesia. Juxtacellular recordings were performed
from motor and somatosensory areas of the cortex. Simultaneous dual
intracellular recordings in parallel with local field potential recordings
from cortical (motor cortex) and thalamic (VL nucleus) areas were carried
out to assess the temporal relationships between thalamic and cortical
activities during spindles. A biologically plausible neuronal network
model of the thalamocortical loop was constructed to investigate the
relative contribution of thalamic and cortical factors in spindle termination.
Thalamocortical and thalamic reticular neurons were modeled
along with the cortical pyramidal neurons and inhibitory interneurons.
Each neuron consisted of a dendritic and an axosomatic compartments,
and was embedded with specific ion channels all following Hodgkin-
Huxley kinetics. Synaptic connections were represented by AMPA-,
NMDA-, GABAa-, and GABAb-type of receptors. The spatial patterns
of synaptic afferents and efferents were stochastically distributed as observed
biologically.
Results: Desynchronization of firing between thalamic and cortical
neurons was found to be a primary mechanism for spindle termination
complimented by h-current upregulation. It leads to cortical spiking after
rebound burst in the thalamus, which prevents T-channels de-inactivation
and promotes spindle termination.
Conclusion: The cortical feedback actively influences the termination
of sleep spindles in vivo. The cortex can control the duration of spindles,
in contrast to the view that sleep spindles are purely controlled by intrinsic
thalamic properties.
Support (If Any): This study was supported by NIH-NIBIB (Grant
1R01EB009282-01).
0106
THE HUMAN BRAIN’S RESPONSE TO AUDITORY
STIMULATION VARIES WITH THE PHASE OF SUB-1HZ
OSCILLATION IN NON-REM SLEEP
Sheth B 1,2 , Bendele T 1
1
Electrical & Computer Engineering, University of Houston, Houston,
TX, USA, 2 Center for NeuroEngineering and Cognitive Science,
University of Houston, Houston, TX, USA
Introduction: During non-REM sleep, the brain oscillates at a frequency
< 1Hz. Alternating up and down states of these slow wave oscillations
correspond to depolarization and hyperpolarization of neurons and
A39
SLEEP, Volume 34, Abstract Supplement, 2011