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Stewart Heitmann
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Welcome to my Google+ site. This where I post items of personal interest. My research publications are hosted on a different site. You can find those at http://stewart-heitmann.ego.id.au.
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I made the design on these tiles for my mother's 90th birthday. They commemorate playing draughts with her when I was a boy. The design has one draught piece for each member of the family. Boys in black, girls in white.
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Botany Bay, Australia.
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Botany Bay, Australia.
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Wollemi National Park, Australia.
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The cover artwork to my book is a tiny detail from my "Fone Books" painting (another post in this collection) with digitally enhanced colours. It even looks like a slice of brain tissue in places, which is a happy coincidence.
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Optogenetic techniques allow neuroscientists to stimulate neurons directly with light. It has become a popular method for probing neural function in living animals. But does optogenetically stimulated tissue operate with normal neuronal dynamics? Recent observations of optogenetically-induced gamma waves in macaque cortex provide us with a surprising clue that it is only apparent with mathematical neuroscience.

Neuroscientists at Brown University recorded the local field potential (LFP) of macaque cortex in the immediate vicinity of optogenetically stimulated tissue. They found that gamma oscillations (40-80Hz) emerge from the stimulation site in a manner consistent with Type 2 neural excitability (where neurons act as resonators). They also found that the gamma oscillations propagate away from the site as travelling waves.

The observations are puzzling because theory predicts that travelling waves are only supported by Type 1 neural media (where neurons acts as integrators). The apparent contradiction was resolved by modelling the cortex as a Wilson-Cowan neural field. Such models mimic either Type 1 or Type 2 neural media depending upon the choice of parameters. It was found that targeted stimulation of the inhibitory cells can locally transform the neural field from Type 1 to Type 2. The neurophysiological data could thus be explained by optogenetic stimulation which predominantly recruits inhibitory cells.

The model illustrates how the act of optogenetic stimulation can substantially alter the dynamical properties of the neural tissue being studied. The findings are published in PLOS Computational Biology.

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Gunbower National Park, VIC, Australia
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Washington Monument. Looking Up.
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Voluntary muscle movement is known to coincide with changes in the 20-30 Hz oscillations in electrical recordings of both the brain (EEG) and the muscle (EMG). This computational model published in the Journal of Neurocomputing shows how the descending motor tract can translate patterns of oscillations in motor cortex into patterns of muscle contraction in a simulated limb. It offers a new perspective on the functional role of oscillations in motor control.

http://www.sciencedirect.com/science/article/pii/S0925231215008814
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