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Lecture 7

PSY290H1 Lecture Notes - Lecture 7: Action Potential, Lidocaine, Bregma

Course Code
Suzanne Wood

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October 2 2018
Stereotaxic surgery:
This device allows you to position the head in a certain orientation and adjust. Orients
you and allows you to hit the target location.
On the right: more details for experimental work using stereotaxic surgery in rodents.
It shows that:
-There is a brain atlas, where you flip through a chart and find coordinates for the
location you want to get to
-The numbers you get are all in orientation to bregma, the seams in the skull of a rodent
-Then you drill holes in the skull
There’s multiple ways of creating lesions:
-aspiration: gentle sucking pressure that removes cells. This is what they do in humans.
-Radio frequency: creates heat around the electrode and the heat destroys the nearby
-Sectioning: cutting with the electrode
-There is also a reversible way: lidocaine. A synthetic drug. It can shut down your
voltage gated sodium channels. It numbs that area of the brain, shuts that area down.
It’s reversible bc when the lidocaine wears off, that tissue is fine- meaning that animal
can also serve as its own control.
-But the drawback is that it spreads, so it cant be just that area.
However, you need to be careful when interpreting results, esp with the irreversible
lesions: perhaps it’s the connections b/w diff parts of the brain that are crucial for that
function and not that area itself. How can you be sure that you’re not lesioning the
connections passing through?
Using stereotaxic surgery, you can do lesion studies and drop down electrodes and
record neurons.
But lesions damage the brain. What if you just want to listen? Electrophysiological
- Intracellular unit recording: inside the cell, intra. It’s less common if we’re looking at
- Extracellular unit rec: dropping your electrode in but not penetrating the neuron, but
listening right next to it. The data you’re generating; every AP that’s fired, you get a tick
mark. From here, you can get the frq at which the neuron is firing.
- Multiple unit recording: recording from multiple neurons at once. Instead of dropping
electrode down and listening to just neuron, you’re agnostic to the number of neurons
you’re recording from. Recording from several neurons at once. You’re just looking at
the overall activation of that area of the brain over time.
- Invasive EEG recording: similar to EEG on scalp, but that one’s not invasive. Stick eeg
strips right onto the cortex- here there’s less interference so there’s better localization.
There’s no big buffer of the skull and derma mater etc.
C: on top, a set of action potentials, right after one another. Below that are the tick
marks. The “spike train”. Each spike is an AP and this is a train of spikes.
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