Lecture 17- Neural Representations

What is synaptic transmission?

The process by which neurons communicate, where an action potential in a presynaptic neuron triggers the release of neurotransmitters that influence a postsynaptic neuron.

How many neurons can a single neuron receive input from?

A neuron can receive input from thousands of other neurons.

What happens when sufficient input reaches a postsynaptic neuron?

It can trigger an action potential, propagating the signal down the axon.

What is an action potential?

A rapid, transient change in the membrane potential of a neuron; the neuron is said to have “fired.”

How is firing rate expressed in neurons?

As spikes per second, e.g., 10 spikes/sec = 10 action potentials per second.

What normally causes action potentials?

Sufficient excitatory input, such as sensory stimuli, e.g., whisker touch in a rat’s somatosensory neuron.

What is single-cell recording?

A method to measure action potentials from individual neurons while stimuli are presented.

What is a neuron’s receptive field?

The specific area of space or set of stimuli that evokes firing in that neuron.

How are action potentials represented in single-cell recordings?

As vertical lines, with denser lines indicating higher firing rates.

What does single-cell recording tell us about neurons?

It identifies which stimuli cause a neuron to fire and its receptive field.

What is a topographic map in the brain?

An organized representation of sensory or motor space within a brain region.

How is the visual field represented in primary visual cortex?

Through retinotopic maps, where the spatial arrangement of neurons mirrors the visual field.

How can fMRI be used to study neural representations?

By measuring changes in metabolic activity proportional to neuronal firing, revealing population-level activity.

Approximately how many neurons in visual cortex represent a single visual image?

At least 200 million neurons.

What is the principle behind tonotopic maps in auditory cortex?

Neurons are organized according to the frequency of sound they respond to.

How are odors represented in the olfactory bulb?

Different scents evoke distinct spatial patterns of neural activation.

What role do topographic maps play in the somatosensory cortex?

They mirror the layout of the body, allowing precise sensory perception.

What role do topographic maps play in primary motor cortex?

They reflect the body’s layout for precise motor control.

What is the role of neurotransmitters in synaptic transmission?

They carry chemical signals from presynaptic to postsynaptic neurons across the synapse.

What are presynaptic and postsynaptic components?

Presynaptic: axon terminal releasing neurotransmitters; Postsynaptic: dendrites or soma receiving signals.

What happens at the synapse?

Electrical signals in the axon are converted to chemical signals and then back to electrical signals in the postsynaptic neuron.

What is the difference between single-cell recording and fMRI?

Single-cell recording measures individual neuron activity; fMRI measures large populations and metabolic activity.

Why are topographic maps important for neural computation?

They enable efficient encoding, perception, and action planning.

What is retinotopy?

The spatial mapping of the visual field onto neurons in the visual cortex.

How is activity in the olfactory bulb used for discrimination?

Distinct spatial patterns of activity allow discrimination between different scents.

What is the key difference between receptive fields and maps of neural activity?

Receptive fields describe single neuron response regions; maps show population-level organization.

How do neurons in visual cortex respond to stimuli?

Only neurons whose receptive fields overlap the stimulus location will fire.

How does fMRI estimate the number of neurons involved in a task?

By measuring blood flow and metabolic activity correlated with neuronal firing.

What is the relationship between single-cell firing and perception?

Patterns of firing in populations of neurons encode sensory information for perception.

What is the significance of topographic organization across sensory modalities?

It ensures that the brain maintains spatial fidelity, allowing precise integration of sensory input and motor output.