{ "cells": [ { "cell_type": "code", "execution_count": null, "id": "d99c3852", "metadata": {}, "outputs": [], "source": [ "%load_ext autoreload\n", "%autoreload 2" ] }, { "cell_type": "markdown", "id": "a0dd997d", "metadata": {}, "source": [ "# Event Related Potentials (ERPs)" ] }, { "attachments": {}, "cell_type": "markdown", "id": "54ef10ea", "metadata": {}, "source": [ "## Getting Started\n", "\n", "*Please Note* this tutorial is a work in progress. Not all features from the original [HNN-GUI](https://jonescompneurolab.github.io/hnn-tutorials/erp/erp) are reproduced here.\n", "\n", "In order to understand the workflow and initial parameter sets provided with this tutorial, we must first briefly describe prior studies that led to the creation of the provided data and evoked response parameter set that you will work with. This tutorial is based on results from our 2007 study where we recorded and simulated tactile evoked responses source localized to the primary somatosensory cortex (SI) [1]_.\n", "\n", "In our 2007 study, we investigated the early evoked activity (0-175 ms) elicited by a brief tap to the D3 digit and source localized to an an equivalent current dipole in the contralateral hand area of the primary somatosensory cortex (SI) [1]_. The strength of the tap was set at either suprathreshold (100% detection probability) or perceptual threshold (50% detection) levels (see Figure 1, left panel below). Note, to be precise, this data represents source localized event related field (ERF) activity because it was collected using MEG. We use the terminology ERP for simplicity, since the primary current dipoles generating evoked fields and potentials are the same.\n", "\n", "We found that we could reproduce evoked responses that accurately reflected the recorded waveform in our neocortical model from a layer specific sequence of exogenous excitatory synaptic drive to the local SI circuit, see Figure 1right panel below. This drive consisted of “feedforward” / proximal input at ~25 ms post-stimulus, followed by “feedback” / distal input at ~60 ms, followed by a subsequent “feedforward” / proximal input at ~125 ms (Gaussian distribution of input times on each simulated trial). This sequence of drive generated spiking activity and intracellular dendritic current flow in the pyramidal neuron dendrites to reproduce the current dipole signal. This sequence of drive can be interpreted as initial “feedforward” input from the lemniscal thalamus, followed by “feedback” input from higher order cortex or non-lemniscal thalamus, followed by a re-emergent leminsical thalamic drive. Intracranial recordings in non-human primates motivated and supported this assumption [2]_.\n", "\n", "In our model, the exogenous driving inputs were simulated as predefined trains of action potentials (pre-synaptic spikes) that activated excitatory synapses in the local cortical circuit in proximal and distal projection patterns (i.e. feedforward, and feedback, respectively, as shown schematically in Figure 1 right, and in the HNN GUI Model Schematics). The number, timing and strength (post-synaptic conductance) of the driving spikes were manually adjusted in the model until a close representation of the data was found (all other model parameters were tuned and fixed based on the morphology, physiology and connectivity within layered neocortical circuits [1]_. Note, a scaling factor was applied to net dipole output to match to the magnitude of the recorded ERP data and used to predict the number of neurons contributing to the recorded ERP (purple circle, Figure 1, right panel). The dipole units were in nAm, with a one-to-one comparison between data and model output due to the biophysical detail in our model.\n", "\n", "\n", "\n", "