The provided code models a simplified neural circuit in the olfactory bulb, a part of the brain responsible for processing smell information. The biological basis centers around interactions among key cell types in the olfactory bulb – olfactory sensory neurons (OSNs), mitral cells, and granule cells – capturing aspects of synaptic excitation and inhibition that shape odor processing.

Biological Components

1. Olfactory Sensory Neurons (OSNs):

   • OSNs are modeled as ThetaStim objects that simulate input to the olfactory bulb from the nose, representative of breathing or light stimuli, which is crucial for odor detection.
   • These sensory inputs are wired to mitral cells, mimicking how spatial and temporal patterns of OSN activity convey odorant information.

2. Mitral Cells:

   • Mitral cells are principal neurons in the olfactory bulb that receive direct excitatory input from OSNs.
   • They are represented by the Mitral objects (m1, m2), and their dendrites receive ThetaStim input through synaptic models (AmpaNmda).
   • The code simulates excitation of mitral cells at the tuft dendrite region, where OSNs typically synapse, to mimic sensory input’s excitatory effects.

3. Granule Cells:

   • Granule cells are inhibitory interneurons connected to mitral cells via dendrodendritic reciprocal synapses allowing bidirectional communication.
   • Modeled as Granule object (gc), the connections between mitral cells and granule cells involve both excitatory (using AMPA/NMDA synapses) and inhibitory effects (FastInhib), closely representing biological lateral inhibition seen in the olfactory bulb.

Synaptic Dynamics

• Excitatory Synapses: The AmpaNmda model simulates AMPA and NMDA receptor-mediated excitatory synaptic transmission, typical in fast excitatory synapses in the central nervous system.
• Inhibitory Synapses: The FastInhib model represents GABAergic inhibition, capturing granule cell output, which traditionally provides feedback inhibition to mitral cells.

Network Dynamics

• ThetaStim Inputs: This element models both rhythmic (e.g., respiration-coupled) activity affecting mitral cells, incorporating the biological feature of olfactory processing linked with breathing rhythms.
• Dynamic Control: Adjustable synaptic weights and control panels allow simulations of various input conditions, capturing the flexibility of biological systems to respond to different sensory regimes.

The biological model captures essential dynamics within the olfactory bulb: the integration of sensory inputs by mitral cells and the modulation of these signals through inhibitory feedback from granule cells. This interplay is fundamental for the temporal and spatial refinement of odor signals before they are relayed to higher brain regions for further processing.