Neuroscience

First, the brain is organized into functionally specific areas, and second, neurons in different parts of the vertebrate nervous system, indeed in all nervous systems, are quite similar. Small comparison with Computers A gross observation between computer’s transistors and human neurons is that there a big difference of numbers: trillions of transistors vs billions of neurons. 6 orders of magnitude frequency difference. Many many neural types and different types of connections. And the digital vs analog and chemical modes of communication. Parallel processor abilities. Fixed vs plastic architectures But this is comparing with transistors with one higher level object, so this comparison might not be completely fair. And only some brain areas are similar to real neural networks ...

Synapses are the connections that exist between one neuron and another, so we can think of them as the communication channel between neurons. Gap Junctions Electrical based 🟩 These are also called Gap Junctions These are more direct connections between neurons, allowing excitation ions to pass through quite directly (this is the difference compared to chemically based ones). It’s a circuit more similar to an electronic one because it’s faster. Another characteristic of these kinds of synapses is that they are two-way channels. ...

In general we want to understand how neurons encode the rate and temporal information to build specific features like place cells, grid cells, velocity, head direction, or how it can guide behaviour or coordination. Many neurons encode together some features, it is quite rare that you have the face neuron and similars. Imaging techniques help us to get more information about these parts. The basic idea is to have one first lens that makes an object bigger but inverted, and another lens, called the eyepiece that sees the original part bigger, and in correct shape. With some high school physics is possible to compute how much is the enlargement due to the lens. ...

Associative Conditioning Classical Conditioning Pavlov’s experiment He was interested in digestive systems of dogs. Then he notices that if we show food to dog, they start to salivate. If paired with sound (tuning fork) they start to salivate even if they just hear the sound. He defines two states: Before conditioning During conditioning After conditioning state. Important words are conditioned stimulus, conditioned response. And their oppose (unconditioned). It is important that it is quite consistent. Associate unconditioned stimulus with conditioned stimulus. ...

Humans are not rational. See (Dostoevsky 1864), the parable of the destroying free will. In this note we will describe some behavioural economics ideas that could be interesting in this side. Economical Games The rules of the Ultimate game The proposer makes an offer as to how this money should be split between the two. The second player (the risponder) can either accept or reject this offer. If it is accepted, the money is split as proposed, but if the risponder rejects the offer, then neither player receives anything. ...

This note is just a collection of past useful notes to know to apply machine learning methods for the analysis of topics interesting in the neural sciences. Estimators You need to know all Parametric Modeling. We want to estimate unknown random variables with some observations. Maximum Likelihood See Bayesian Linear Regression. Bias-Variance Decomposition Fisher Information See Parametric Modeling#Fisher information. Applications Echo-locating bats Bats use echo location to locate the target, a platform. Bats use to click slightly left and right compared to their direction of motion. ...

Vision is THE most important sense for humans. Most of the information we get is through vision 90% vision 8% tactile, touch 3% hearing I have no idea how did they measure this aspect. This is true for humans, but for mice for example it is different, they have probably a 64x64 pixel resolution equivalent. For humans, visual data is more important, it is faster compared to speech and other senses. Human vision is estimated to be about 576 Megapixels of data (3M snapshots patched together with saccades, that has that pixel image value), since it can distinguish 0.6arc-minutes (0.01 degrees). There is an estimate of about 60kk rods and 3kk cones. ...

How are inputs made into motion? We analyze feedback systems in auditory systems in birds. Motivation Birds are very good at producing and reproducing songs by moving their vocal cords complexly (sensory motor learning). Birds and Humans do not have much of a common ancestry (last one was fishes). 71% of the birds, both female and male birds sing, for Zebra finch it is a mating behaviour, so only male sing. ...

Here we attempt to answer what is memory, how is it stored and retrieved. Memory is a process by which information is: Encoded Stored Retrieved The brain has different types of memories, and certain brain regions are specialized for this task. Ebbinghaus Curves Other experiments destroy parts of the cortex and correlate this with recall. Types of memory TODO see Kendal67-1 figure. Sensory memory iconic memory (remembering images) 150-500 milliseconds Echoic memory (recognizing some sounds) usually retained for 1 to 2 seconds. This memory is filtered by consciousness/attention to be passed to short term working memory. The register capacity of this memory is considered to be quite large. Short-term memory it has an explicit storage of about 7 +- 2 items (so very small). Depending on attention level, it is retained for 2 to 18 seconds. It seems the representation here is often vocal. ...

The synaptic connections that define such circuits are typically made in a dense tangle of dendrites, axons terminals, and glial cell processes that together constitute what is called neuropil. Knee-Jerk Response The knee-jerk reflex (also known as the patellar reflex) is a classic example of a mono-synaptic reflex arc, which involves a direct connection between sensory and motor neurons, as well as inhibitory circuits to regulate movement. ...