Transcript poster - Stanford University

Gamma-band spike-field coherence in the optic tectum of the barn owl
Sridharan Devarajan, Kwabena Boahen, Eric Knudsen
Departments of Neurobiology and Bioengineering, Stanford University
Summary
Synchronization among
important signature of
known, however, about
underlying the induction
neuronal spikes is known to be an
target selection in primates. Little is
the cellular and network mechanisms
of this synchrony.
Stimulus selection in the optic tectum
Stimulus evoked gamma-band LFP
Being part of the avian gaze control circuitry, the optic tectum
(OT) is ideally suited for stimulus selection. Its homolog in
primates (superior colliculus, SC) is known to contribute
importantly to spatial attention (Muller et al, 2005).
Spatial tuning
Neurons
LFP spectrogram
Retina
E Excitatory
I
Optic Tectum
Using recordings of single neurons and local field potentials in
the optic tectum of the barn owl (Tyto alba), we find that
gamma-synchrony is a signature of stimulus selection and
distractor suppression.
Inhibitory
Isthmotectal microcircuit
I
By modeling the tectal circuit in-silico, on neuromorphic
hardware, we show that mimicking the effects of
neuromodulation by acetylcholine is a potential mechanism for
evoking synchrony during bottom-up stimulus selection.
I
LFP spectrogram
Layer 4/5
Layer 8/10
E
Contrast response
Imc
This hypothesis predicts that inactivating the Ipc (ACh nucleus)
should disrupt both neural and network signatures:

Contrast response function shifts right (less sensitivity)

Gamma-synchrony reduces (if not eliminated)
Future work will involve testing the key predictions of the model
by inactivating the Ipc, while recording in the OT (in-vivo), as well
as microstimulating Ipc (in-vitro) to test if ACh input to OT can
induce synchrony. The transient increase in synchrony upon
stimulus offset will be incorporated into a revised model.
Acknowledgments
AMPA (excitatory)
GABA (inhibitory)
Ipc
Gaze Control
Image courtesy: Phyllis Knudsen
The cholinergic Ipc circuit, and the GABA-ergic Imc circuit can
be engaged by bottom-up inputs from the retina or top-down
inputs from the forebrain gaze fields (AGF), thereby initiating or
suppressing motor output.
Orienting to salient stimuli in
the environment (e.g. sudden
appearance of a predator)
We hypothesize that neuronal and network signature of attention
are linked by ACh neuromodulation
Synapses
Attention
Maintenance of a “goal” in
working
memory
(e.g.
distinguishing food from dirt)
Key Predictions and Future directions
Modeling the circuit in-silico
Target Enhancement
Spatial tuning
Contrast response
ACh (cholinergic)
ACh input from Ipc to OT facilitates fast excitatory (AMPA)
synapses from the retina onto both excitatory (E) and inhibitory
(I) neurons.
We model a single column in OT with spatially localized RF on
a neuromorphic chip with 1024 excitatory and 256 inhibitory
neurons.
Distractor Suppression
Neuron
Chip
Here we focus on the neural mechanisms of bottom-up
stimulus selection, a fundamental component of attention.
Arthur & Boahen, 2007
Neuronal signature
Neuronal signatures
The Ipc circuit is well-placed to
enhance the representation of
target stimuli.
This work was supported by grants NIH1 R01-DC00155-25 (EK) and
the NIH Director’s Pioneer Award Program Grant DPI-OD000965
(KB). SD wishes to thank John Arthur for his help with
programming the chip, and Alex Goddard and Phyllis Knudsen for
kindly sharing images. Spectral analyses were performed with the
Chronux toolbox (www.chronux.org)
Literature Cited
• J. V. Arthur, K. A. Boahen, IEEE Trans. Neural Netw. 18,
1815 (2007).
• H. Luksch, Rev. Neurosci. 14, 85 (2003).
• J. R. Muller, M. G. Philiastides, W. T. Newsome, Proc.
Natl. Acad. Sci. U. S. A. 102, 524 (2005).
• T. Williford, J. H. R. Maunsell, J. Neurophysiol. 96, 40
(2006).
Network signature
The Imc circuit is well-placed to
suppress the representation of
distractors (red).
In-vivo
Facilitation of excitation
Detailed isthmotectal neuroanatomy
Facilitation of inhibition
Retina
Retina
I
Enhanced firing rate, and
sharpened receptive field
(RF)
?
Reduced threshold and
increased sensitivity
L-8
E
L-8
L-4
E
Network signatures
In collab. with: Shreesh Mysore
40x
4x
Image courtesy: Alex Goddard
Spikes synchronize
phase lock with LFP
and
LFP shows strong gamma
(γ) rhythm (30-90Hz)
Previous models have attempted to link these two signatures
of attention, but have ignored the underlying neural circuitry.
In-silico
Ipc (green, biocytin) projects homotopically to the optic tectum
(arrow, insert), terminating in layer 5, rich with inhibitory neurons
(red, calbindin). These interneurons have widespread horizontal
arbors. Excitatory cells (blue, DAPI) in layers 8-10 also send
their dendrites up into layer 5.
Retinal axons synapse onto both excitatory and inhibitory
neurons in layers 1-5 (Luksch, 2003).
Data courtesy: Alex Goddard
Data courtesy: Alex Goddard