Neural Circuit Simulation: Logic Gates

This interactive application simulates how biological neurons can be connected to perform basic computational logic, mirroring the function of electronic logic gates (AND, OR, NOT).

How to Use

1. Select a Step: Use the buttons at the top of the screen to navigate through the 5 different simulation steps.
2. Read the Instructions: The box below the buttons will update with specific instructions and expected observations for the current step.
3. Interact: Click on the yellow "Input Boxes" (A and B) on the left side of the screen to send an electrical signal (action potential) down the pre-synaptic neurons.
4. Observe: Watch the live graphs to see the membrane potential change in real-time. Notice how the post-synaptic neurons react based on the specific synaptic configurations of that step.

Visual Guide

• Yellow Boxes: Sensory inputs. Click these to trigger a signal.
• Green Neurons: Pre-synaptic neurons (inputs).
• Blue Neurons: Post-synaptic neurons (outputs).
• Yellow Dots: Excitatory neurotransmitters (cause depolarization).
• Red Dots / Red Flashes: Inhibitory neurotransmitters (cause hyperpolarization).
• Live Graphs: Display the membrane potential in millivolts (mV). The red dashed line represents the threshold (-55mV) required to fire an action potential.

Essential Theory: Combining Logic Gates

In computer science and digital electronics, the AND, OR, and NOT gates are the fundamental building blocks of all computation. When you understand how to create these three behaviors (as demonstrated in your neural simulation), you theoretically have the power to compute anything.

The Power of Combinational Logic By wiring these basic gates together, you can create entirely new logic functions. Because your neural simulation proves that biological synapses can execute AND, OR, and NOT functions, it implies that networks of neurons are theoretically capable of universal computation, functioning similarly to the microchips inside a computer.

Simulation Assumptions

To make this biological simulation function smoothly as a demonstration of discrete logic, several physiological assumptions and simplifications are programmed into the code:

General Assumptions:

Resting & Threshold Potentials: The resting membrane potential of all neurons is assumed to be -70mV, and the threshold required to fire an action potential is strictly set at -55mV.

Instantaneous Transmission: While action potentials have travel time in real life, the simulation simplifies propagation speed for visual clarity.

Step-Specific Assumptions:

Step 2 (Simple Synapse): It is assumed that four simultaneous synaptic connections releasing excitatory neurotransmitters are exactly enough to depolarize the post-synaptic neuron by 15mV (from -70mV to -55mV), triggering an action potential.

Step 3 (AND Gate / Spatial Summation): The synaptic weights from inputs A and B are halved. It is assumed that Input A only has two synapses and Input B only has two synapses connected to Neuron 2. Therefore, clicking only A results in a subthreshold Excitatory Postsynaptic Potential (EPSP). Firing A and B simultaneously (Spatial Summation) provides the combined four synapses necessary to reach the -55mV threshold.

Step 4 (OR Gate): The synaptic connection strength is maximized. It is assumed that Input A and Input B both have four synaptic connections to Neuron 2. Therefore, a signal from either pathway independently is strong enough to cross the threshold.

Step 5 (NOT Gate / Inhibition): Two major assumptions are made here:

Pacemaker Activity: The post-synaptic neuron is assumed to have "pacemaker" properties, meaning its resting membrane potential naturally creeps upward until it fires automatically, representing a baseline "HIGH" (1) output.

Inhibitory Postsynaptic Potentials (IPSPs): The pre-synaptic neuron (Input A) is assumed to be an inhibitory interneuron. It releases inhibitory neurotransmitters (like GABA) that forcefully hyperpolarize the post-synaptic neuron (-15mV per synapse), driving it away from the threshold and successfully pausing the pacemaker from firing. This creates the "NOT" inversion.