Simple Rod Photoreceptor Circuit

One NeuroBytes rod photoreceptor is connected from the dark output through an excitatory neurotransmitter cable to a short interneuron dendrite. In the dark, the interneuron fires regular action potentials. As the flashlight beam sweeps across the rod photoreceptor light detector, the action potentials slow and then stop. This happens because the dark output is inactive in the light. Real rod photoreceptors work in a similar way, releasing neurotransmitters in the dark, and reducing their release in the light.

Disinhibition

Disinhibition circuits are thought to be important for learning and memory, amongst other neurological functions. You can model this phenomenon in several way using NeuroBytes, including the circuit in the video below. The irregular interneuron firing is determined by the interplay of excitation and inhibition from the two tonically active neurons (TANs). If the TAN on the left is inhibited by a sensory neuron (pressure sensory neuron in this example), the interneuron becomes disinhibited and begins to fire in time with the right TAN.

Can you build other NeuroBytes circuits that produce similar behaviors?

Interneuron Potentiation

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Neurons are though to encode memories by changing the strength of synapses. Very generally, the more a presynaptic neuron signals a postsynaptic neuron, the more likely that postsynaptic neuron is to fire an action potential in response to future signaling. NeuroBytes interneurons incorporate this kind of synaptic potential to encode memories. When in memory mode, high frequency input signals increase interneuron synaptic strength, and make the neuron more likely to fire an action potential in response to future inputs. This is indicated by a magenta LED that increases in brightness to indicate the level of potentiation.

Insecure NeuroBuggy

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When Insecure is put down in an open area, the right wheel only will be moving forward, and the NeuroBuggy will be driving in counter-clockwise circles. If it is put down with a wall on its left however, the NeuroBuggy will move forward and left, bumping into the wall. This will activate the Touch Sensory Neuron on the left front of NeuroBuggy, which will activate the left Motor Neuron, and cause the left wheel to rotate forward. This will move the NeuroBuggy slightly away from the wall, deactivating the Touch Sensory Neuron, and the cycle begins again.

Paranoid NeuroBuggy

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Paranoid has 1 rod photoreceptor that it uses to navigate its environment. It uses two interneurons and two motor neurons to do so, but the two sides of the circuit are connected a bit differently. The "light" output on the rod drives both wheels forward, while the dark output drives just the left wheel backward. This results in a NeuroBuggy that follows the edge of a light halo.

Stubborn NeuroBuggy

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Stubborn has paired two neuron oscillators on it. When the front touch sensory neuron is activated, the touch inhibits the "forward" oscillator and activates the "backwards" oscillator. When the rear touch sensory neuron is activated, the opposite happens. This circuit causes the NeuroBuggy to run back and forth between two objects.