Learning Diary, Week 2

Action potentials are foundational to the electrical flow of information in the nervous system, and are broken down into discrete steps, which all take place in less time than the blink of an eye:

Resting potential is around -64mv, and is defined by the potential difference between ions on the inside and outside of the membrane. Potassium and sodium are distributed on concentration gradients across the inside and outside of a membrane, with more sodium on the outside, and more potassium on the inside. This equilibrium is maintained via sodium-potassium pumps.

Action potentials are said to be “all or none” because a threshold has to be reached in order to trigger them. What this means practically is that enough voltage-gated sodium channels need to open so that sodium ions can rush into the cell, causing the rising phase, when the membrane depolarizes.

Overshoot occurs when the inside of the neuron is positively charged in relation to the outside, caused by the rush of sodium ions from the rising phase. When measured by an oscilloscope, this is the peak of the action potential waveform.

The falling phase is the part of the waveform in the life of an action potential when the line descends into a negative potential once again. This is caused by potassium leaving the neuron through voltage gated potassium channels, which open after an initial delay.

Voltage-gated potassium channels remain open when there is low sodium permeability, which is responsible for the undershoot, or hyperpolarization phase of an action potential.

Action potentials can be stimulated in a lab setting via sending out an electrical signal via electrode. The higher the frequency, the higher the firing rate of action potentials. When hooking up the resulting waveforms to loudspeakers, actions potentials reportedly sound “like popcorn,” this makes sense from looking at the waveform shape, and knowing how quickly they occur. I wonder what a more elaborate system of neural activity would sound like.

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Neuron Doctrine

Here is my drawing for the first “Structure and operation of the human brain” exercise, I was so proud of it that I hung it on the fridge and am now posting it on this blog 🙃

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Minimalist Mouse Rave (Learning Diary, Week 1)

In the 19th century people started to think of “nerves as wires,” which corresponded with electrical discoveries occurring around the time. I’m primed to think about electrical systems in musical terms, such as through the input/output and signal generation/modulation systems of synthesizers. It’s fascinating to me, then, to understand how similar the tools are for measuring the electricity generated by a neuron, to the those used in analogue electronic instruments and DIY electronics.

While reviewing the structures that comprise brain cells, I learned that neuronal shape can be regulated by various signals within the neuron, and that microtubules are part of the structure of neurites. MAPs (microtubule associated proteins) help keep microtubules together and connected with other parts of the neuron, although many MAP functions are not yet known. Changes to the axonal area of MAPs are called tau, and these show up in Alzheimer’s disease.

I happened to hear an interview with neuroscientist Li-Huei Tsai on the pop science podcast “Radiolab” with recent updates on her research of Alzheimer’s in animal models. Tsai and her team had flashed light at 40hz, or the “gamma frequency” (which is present in brainwave patterns during focused states) to mice in early stages of the disease. This non-invasive measure significantly increased microglia (referred to as “janitor cells” in the podcast) in the visual cortex, impacting the pathology.

My first thought when learning this, is that you could also play a sine wave at 40hz (with an adequate subwoofer) and complete the minimalist-mousey-rave. Turns out, this is what the update was about and there is a recent paper demonstrating the outcomes with auditory and multi-modal (audio-visual) inputs.

In short: auditory exposure to gamma frequencies over 7 days improved memory and spatial recognition while reducing amyloid in the auditory cortex and hippocampus, and reducing phosphorylated tau. The combination of audio and visual stimuli caused “microglial clustering” and reduced amyloid in the medial prefrontal cortex (Martorell et. al, 2019)

It’s fascinating that these simple tools can have a direct effect on a cellular level, but then it’s also intuitive, because our brains are constantly being changed by our sensory interaction with the outside world. Approaching my study of neuroscience through a sound/new media background, it’s neat to see (and hear) where the two fields intersect.

Sources cited:

WNYC Studios. 2020. Bringing Gamma Back, Again | Radiolab | WNYC Studios. [online] Available at: <https://www.wnycstudios.org/podcasts/radiolab/articles/bringing-gamma-back> [Accessed 13 September 2020].

Martorell, A., Paulson, A., Suk, H., Abdurrob, F., Drummond, G., Guan, W., Young, J., Kim, D., Kritskiy, O., Barker, S., Mangena, V., Prince, S., Brown, E., Chung, K., Boyden, E., Singer, A. and Tsai, L., 2019. Multi-sensory Gamma Stimulation Ameliorates Alzheimer’s-Associated Pathology and Improves Cognition. Cell, 177(2), pp.256-271.e22.

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Hello world!

Welcome to Aalto. This is your first post. Edit or delete it, then start blogging!

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