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🎤 Vocab

❗ Information

Methods

Non-invasive bulk tisue imaging in vivo

fMRI - surrogate for blood flow, measures BOLD
Single cell electrophysiology in vitro
Resort to animal models - rats, mice (more mice now because of genetic engineering)
Recently, became possible in human brain

Microwire recordings in Humans

Epilepsy patients, candidates for epilepsy surgery

64-128 microwires (40 um diameter) able to record single neuron activity and LFPs
- “Depth electrodes”
Effective recording bandwidth DC - 9 kHz

Intracranial Electrode Implantation

Region of Interest (ROI):

MTL - Most frequent cause of focal epilepsy
- Likely due to feedback architecture, in HIP

Patients usually only participate, because they’re bored otherwise
The experiments can’t be interesting (because they have to repetitive and designed to allow statistics), but patients are excited for small talk before and after

Spike detection and Spike Sorting

Can separate spikes depending on size, shape, and timing (think of distance from recorder, and originating neuron spike differences)

Distributed Coding vs Sparse Coding

Distributed Coding - Combinations of neurons representing itself
Sparse Coding - One neuron represents something itself, grandmother cell

Concept Cell

Neuron that fires in response to Marilyn Monro
Also, same type of cell that:

Fires for image of Michael Ballack, his written name, and name spoken by computer voice, while not firing for nearly anything else

These “semantically invariant concept cell” have only been found:

In humans (difficult to prove semantic understand in animals)
In temporal lobe

Domain Specificity

Human amygdala encodes person identity, not gaze

Response Latencies:

About twice as long to response as non humans

Hypothesis:

What is function of these concept cells?

MTL is essential for episodic memory encoding
Responses too late for object recognition
Responses follow conscious, subjective perception
Semantically invariant neurons (‘concept cells’) as building blocks for episodic memory
Sparse coding allows for simultaneous activation

Some things are difficult to disentangle experimentally, so use DRUGS
“Pharmacological Manipulation”

Subjective observed effects of Propofol - Feel a little tipsy, euphoric, talkative, hard to focus on task

Previous study gave a target of 1.5ml of propofol, so they used that

Response under propofol is delayed, and ‘blurred’ out

Concept cells - independent, very different from rodent place cells

Stay stable over test time course of 2 weeks, no knowledge over time course of a year

Summary

Explicit, selective, and invariant single-neuron representations of familiar concepts/persons in the human temporal lobe (“concept cells”)
Concept cells show semantic tuning and are context-independent
Representations follow conscious, subjective perception rather than the physical stimulus, with a posterior-anterior anatomical gradient
Activity of item neurons in the hippocampus, amygdala, and EC determines successful long-term memory encoding of specific items.
Activity of location neurons in the PHC determines successful long-term memory encoding of specific locations.
Concept cells as semantic building blocks for episodic memory

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