The provided code is a computational model designed to examine neuronal spiking probability in response to synaptic input, with specific reference to whisker-mediated sensory input. Below is the biological basis of the key aspects modeled within the code: ### Biological Basis #### **Synaptic Input and Neuronal Response** The code centers around the concept of synaptic input integration in neurons, which is fundamental to understanding how neurons process information. Specifically, it models the probability of spiking (action potential generation) in response to excitatory synaptic inputs. These inputs are presumably glutamatergic, as is typical in excitatory synapses in cortical structures. #### **Whisker Stimulation** The code references different whisker types ('PW', 'SW', 'E2'), suggesting a focus on the rodent whisker-barrel system. In rodents, each whisker is associated with a specific barrel in the somatosensory cortex, forming a well-studied model for sensory processing. Whisker stimulation evokes patterns of synaptic input that can be spatially and temporally organized across cortical columns. The whisker type likely influences the synaptic input parameters due to differences in the density and distribution of synapses associated with each whisker. #### **Parameters of Input: Synapse Number and Timing** Processes such as synapse number and timing, which are varied in the code, are critical to determining the neuronal output. The number of active synapses and their timing influence the neuron's integration of inputs — factors that determine whether postsynaptic potentials summate to reach the threshold for action potential firing. - **Synapse Number:** This represents the density of synaptic inputs, which could be indicative of the extent of sensory input due to whisker deflection. - **Synapse Timing:** Represents the temporal dynamics of input, crucial for the timing of action potentials. The code suggests that inputs could be designed to mimic realistic synaptic timings that occur during sensory processing. #### **Window of Analysis and Spike Probability** The model calculates spike probability within a specified time window following synaptic input, reflecting the biological process of temporal integration in neurons. This process is integral to action potential generation, where the integration of excitatory postsynaptic potentials over time can lead to neuronal firing if the threshold is crossed. #### **Iso-probability Contours** The model outputs iso-probability contours, which visually represent regions of equivalent spike probability across varying synapse numbers and timings. This is a method to assess the influence of synaptic parameters on neuronal output, helping to understand how sensitive neurons are to different patterns of input — a critical aspect in sensory coding and neuronal response characteristics. ### Conclusion Overall, the code models the interaction between synaptic inputs and neuronal firing in response to sensory stimuli, specifically focusing on the rodent whisker system. It highlights the importance of synapse number and timing in determining the likelihood of action potential generation, which forms the basis for understanding sensory processing and representation in the cortex.