Recording From The Brain

Invasive Recording

• Wire electrodes:
• Glass “wire” with uncovered tip to be inserted in the cortex.
• Researchers/scientists/medical practitioners have to “listen” to the spikes and firing of the neurons.

• Micro electrodes:
• Sharp & brittle
• Neuropixel → From the 384 recordable channels, the highest quality spikes are filtered.
• Multiplexing strategies have to be used since the physical aspect limits the number of mechanical contacts to the backbone of the array.

• From a raw signal the LFP (local field potential, through low-pass filter) and action potentials can be extracted.
• LFP are patterns that govern multiple neurons over time.

Spike Detection

• Window discriminator → Holt ⇒ Diagram explaining the shape of the spike on oscilloscope, based on spatial position in comparison to neuron (axon).

• Power method → see ARMA models!

• PCA → project 4D signal to 2D onto the principal components.

• Matched Filtering → Based on convolution of signal with a template.

• NEO (non-linear energy operator) → run signal through a non-linear function (but be aware of outliers, since the signal gets squared!)

• Wavelets → Narrow wavelets pick up higher-frequencies while wider wavelets are able to pick up lower frequencies.

Spike Sorting

• Mixture of Multivariate t-Distributions.

Electrode Selection

• PSNR avoids a neuron being captured multiple times!