Neuron (nerve cell)

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1. image source

• Brains are composed of billions of neurons.
• Each neuron is a cell that processes and transmits information through electrical and chemical signals

• Constituents of a neuron:
• a cell body (soma),
• a collection of inputs (dendrites), and
• an output (axon)

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dendrites

cell body (soma)

axon

How do neurons communicate?

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3

dendrites

cell body

axon

FIRE

chemical release

The neuraxis in the human brain

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1. woman outline source

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lateral

medial

anterior/�rostral

posterior/

caudal

dorsal/�superior

ventral/�inferior

neuraxis

rostral or�anterior

dorsal

ventral

dorsal

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caudial or�posterior

Transections and Planes

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Major subdivisions of the cerebral cortex

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Image taken from: Gazzaniga, Ivry, Mangun, Cognitive Neuroscience, Figure 2.30, p.50

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Many fields influence neuroscience

• Where does the process of interest occur? Localisation

• What information is represented at each location? Representation

• How can we record and model the data? Technology

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Neuroscience

Neurology

Anatomy

Physiology

Neurophysiology

Chemistry

Computer Science

Data Science

Molecular Biology

Physics

Spatial scales in the brain

image source

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Numbers in the brain (rough estimates)

fact source

• Number of neurons in adult human brain: 8x10¹⁰ (80 billion)
• Number of neurons in adult cerebral cortex: 1.8x10¹⁰
• Number of synapses on typical cortical neuron: 6x10³
• Number of cortical columns: 1x10⁵
• Average loss of cortical neurons: 1 / second
• Total surface area of cerebral cortex: 2.5x10³ cm²
• Thickness of cerebral cortex: 1.5-4 mm

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source: Sejnowski et al 2014

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Single-cell recordings

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• Measuring electrical activity using electrodes placed in or near single neurons
• Animal studies or studies with patients undergoing surgery (e.g. epilepsy)
• Analysis of cognitive functions that can lead to Brain Machine Interfaces (BMI)
• High temporal, low spatial resolution

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→ How do individual neurons encode information?

Electroencephalogram (EEG)

• Measuring electrical activity from neurons that reach the scalp using electrodes placed on the scalp
• Signal is derived from several sources in the brain (coarse sampling)
• EEG reflects many ongoing brain processes
• High temporal, low spatial resolution

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→ How does a very large collection of neurons encode information?

electrodes

EEG signal

Electrocorticography (ECoG)

Image source

• Measuring electric activity using electrodes placed on the surface of the cortex
• Similar to EEG but less signal distortion
• High temporal, low spatial resolution

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→ How does a specific collection of neurons encode information?

Magnetoencephalography (MEG)

Image source

• Electric activity of a neuron causes very small magnetic field changes
• MEG measures this change
• Magnetic field is less distorted then the electric field
• High temporal, low spatial resolution but better than EEG

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Functional Magnetic Resonance Imaging (fMRI)

Image source: 1, 2

• Measuring local variations in cerebral blood flow
• Uses MRI to measure oxygen content of the blood (hemodynamic response)
• Assumption: Increased blood flow to the brain regions that have high neural activity
• Blood oxygenation level-dependent (BOLD) signal: The ratio of oxygenated to deoxygenated hemoglobin
• Low temporal, high spatial resolution

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Growth of fMRI publications over year

Image source

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Do you know any fMRI experiments?

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