SpikeFun 0.82 - Adding Some Brainstem into the Mix...

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Until this version, SpikeFun was able to model mammalian thalamocortical system. Outside influences (e.g. from sensory and brainstem afferents) were modeled by simple current injection into neurons of different thalamic nuclei.

SpikeFun 0.82 brings first (and very early) support for non-thalamic and non-cortical brain region. The first region to be supported is brain stem - starting with Pedunculopontine Tegmental Nucleus (or PPTN). SpikeFun 0.82 has limited support for this nuclei, for example - PPTN cholinergic neurons are currently modeled as glutamatergic/GABAergic (target-specific) as SpikeFun does not support muscarinic and nicotinic receptors yet.

Nevertheless, PPTN region is interesting as it sends large projections to the dorsal thalamus and reticular thalamic nucleus (RTN). Cholinergic cells of PPTN exhibit target-specific action in dorsal thalamus and RTN thanks to different postsynaptic receptors (muscarinic M1 and nicotinic for relay cells, muscarinic M2 for RTN cells) [Sherman and Guillery, 2006]. Final effect of this "mixed" mode of action of PPTN cells is disinhibition of thalamic relay cells and inihibiton of thalamic reticular cells, implicating PPTN cells in awareness, arousal and motivation.

In non-anaesthetised animals and humans PPTN cells are most active during awareness and REM sleep while they are the least active during NREM sleep and they represent one of the key hubs of the ascending arousal system (Saper C. B. et al., 2006). In SpikeFun 0.82 "Brainstem Modulation" slider now directly alters spike-rate of the PPTN cells, simulating the effect of disinhibition of the ascending reticular activation system (ARAS) and "switching" the thalamocortical system from sleep to "awake" mode.

If you watch the visualization progress, you will notice that, while PPTN neurons are active, various thalamic nuclei shift from being rendered in red to blue (and vice versa) - this is the result of inhibition of reticular thalamic neurons and excitation of the relay cells - which, in real life, promote awareness and serve as one of the essential prerequisites for consciousness.

Below image shows SpikeFun 0.82 with the active PPTN neurons:


Below video shows the influence of the PPTN neuron activity on the thalamocortical system: