Studying the effects of thalamic interneurons in a thalamocortical neural mass model

Bond, Tom, Durrant, Simon, O'Hare, Louise , Turner, Daniel and Bhattacharya, Basabdatta (2014) Studying the effects of thalamic interneurons in a thalamocortical neural mass model. In: Annual Meeting of the Organisation for Computational Neuroscience, 26 - 31 July 2014, Quebec City, Canada.

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Neural mass models of the thalamocortical circuitry are
often used to mimic brain activity during sleep and
wakefulness as observed in scalp electroencephalogram
(EEG) signals [1]. It is understood that alpha rhythms
(8-13 Hz) dominate the EEG power-spectra in the resting-state
[2] as well as the period immediately before
sleep [3]. Literature review shows that the thalamic
interneurons (IN) are often ignored in thalamocortical
population models; the emphasis is on the connections
between the thalamo cortical relay (TCR) and the thalamic
reticular nucleus (TRN). In this work, we look into
the effects of the IN cell population on the behaviour of
an existing thalamocortical model containing the TCR
and TRN cell populations [4]. A schematic of the
extended model used in this work is shown in Fig.1.
The model equations are solved in Matlab using the
Runge-Kutta method of the 4th/5th order. The model
shows high sensitivity to the forward and reverse rates
of reactions during synaptic transmission as well as on
the membrane conductance of the cell populations. The
input to the model is a white noise signal simulating
conditions of resting state with eyes closed, a condition
well known to be associated with dominant alpha band
oscillations in EEG e.g. [5]. Thus, the model parameters
are calibrated to obtain a set of basal parameter values
when the model oscillates with a dominant frequency
within the alpha band. The time series plots and the
power spectra of the model output are compared with
those when the IN cell population is disconnected from
the circuit (by setting the inhibitory connectivity parameter
from the IN to the TCR to zero). We observe
(Fig. 2 inset) a significant difference in time series output
of the TRN cell population with and without the IN
cell population in the model; this in spite of the IN
having no direct connectivity to and from the TRN cell
population (Fig. 1). A comparison of the power spectra
behaviour of the model output within the delta
(1-3.5Hz), theta (3.75-7.5Hz), alpha (7.75-13.5Hz) and
beta (13.75-30.5Hz) bands is shown in Fig. 2. Disconnecting
the IN cell population shows a significant drop in the
alpha band power and the dominant frequency of oscillation
now lies within the theta band. An overall ‘slowing’
(left-side shift) of the power spectra is observed with an
increase within the delta and theta bands and a decrease
in the alpha and beta bands. Such a slowing of EEG is a
signature of slow wave sleep in healthy individuals, and
this suggests that the IN cell population may be centrally
involved in the phase transition to slow wave sleep [6]. It
is also characteristic of the waking EEG in Alzheimer’s
disease, and may help us to understand the role of the IN
cell population in modulating TCR and TRN cell behaviour
in pathological brain conditions.

Additional Information:BMC Neuroscience 15, Supplement 1 p219
Keywords:Thalamocortical Circuits, Interneurons, Sleep Rhythms
Subjects:G Mathematical and Computer Sciences > G990 Mathematical and Computing Sciences not elsewhere classified
Divisions:College of Science > School of Engineering
ID Code:17253
Deposited On:24 Apr 2015 11:26

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