Module 2.2 Cockroach electroneurophysiology

Nerve conduction velocity

• speed at which an action potential travels along a nerve fiber

• calculated as distance between electrodes/time delay

Extracellular recording

• Measuring voltage changes outside neurons using electrodes that do not penetrate the cell membrane

• Records the summed electrical fields from many neurons firing, not single action potentials

Spike

A brief, sharp deflection in an extracellular recording that indicates an action potential from one or more neurons

Amplitude histogram

• plot showing the distribution of spike amplitudes in a recording

• Used to identify different neuron types based on the size of their extracellular spikes.

Interspike interval (ISI)

• time between two consecutive spikes from the same neuron

• ISI histograms to analyze firing patterns and directional tuning

Teager Energy Operator (TEO)

• digital signal processing algorithm that highlights regions of a signal with high energy and/or high frequency content

• makes it ideal for detecting action potential spikes.

SpikeID.m

• function that uses the kTEO to detect spikes in extracellular recordings

• Outputs: spike number, peak amplitude, sample location (time stamp), and spike waveform data

k (tuning parameter)

• Adjusts the TEO to be sensitive to specific frequency ranges

• Larger k makes the operator more sensitive to lower‑frequency components

Thresholding (in spike detection)

Applying a minimum value to the TEO output to decide which deflections are true spikes and which are noise

Sensory spines

• Cuticular hair‑like structures on the femur and tibia that act as mechanoreceptors/ allow cockroach to sense physical interactions with environment

• stimulated these spines to record evoked responses

Cerci (singular: cercus)

• Paired sensory appendages on the last abdominal segment, covered in fine hairs

• Air puffs on the cerci were used to evoke activity in the ventral nerve cord.

Ventral nerve cord

• The insect equivalent of the spinal cord, runs along the inside of the ventral body wall

• carries sensory information from the cerci and legs to the central nervous system.

Pyrethrin / Permethrin

• The active insecticidal compounds in Raid®

• alters ion channel activity and action potential firing

Principal Component Analysis (PCA)

• statistical technique that transforms spike waveform data into a new set of uncorrelated variables (principal components) that maximize the variance of the data

• Used to separate spikes from different neurons based on waveform shape

• first few PCs capture majority of variancee

Eigenvectors (coefficients)

• weights used in the linear combination of original waveform points to calculate the principal components

• define the directions in which the data vary the most.

Eigenvalues (variances)

• amount of variance explained by each principal component

• Larger eigenvalues mean that PC captures more of the differences between spike shapes.

Cluster analysis (clusterdata)

A method that groups spikes in PC space based on distance. Spikes with similar shapes end up in the same cluster, representing a single neuron.

spikeCluster.m

• takes the output of SpikeID.m, performs PCA, and clusters spikes into user‑defined numbers of groups (e.g., 16 clusters)

• Outputs: cluster assignment, PCA coefficients, scores, variances

Raster plot

• A figure that displays each spike as a dot on a time axis, with different neurons (clusters) shown in different rows

• Useful for visualizing firing patterns across neurons