Neural Encoding I: Firing Rates and Spike Statistics

These flashcards cover key concepts from the lecture on neural encoding, focusing on firing rates, action potentials, and the statistical properties of neuron firing.

What is an action potential?

An action potential is a roughly 100 mV fluctuation in the electrical potential across a cell membrane, lasting approximately 1 ms.

What are 'spikes' in neuroscience?

Spikes are another common term for action potentials, the primary signals used for communication between neurons.

How do neurons transmit information through time?

Neurons transmit information by firing sequences of spikes in various temporal patterns.

Define Neural Encoding.

Neural encoding refers to the map from stimulus to response, cataloging how a neuron reacts to different stimuli.

What is the resting membrane potential of a neuron?

The resting membrane potential is typically about -70 mV relative to the surrounding extracellular medium.

What serves as the reference point for measuring a neuron's potential?

The surrounding extracellular medium serves as the ground or reference point (0 mV) for these measurements.

Which structures control the movement of ions across the cell membrane?

Ion channels are the physiological specializations that regulate the flow of ions to control membrane potential.

What is Depolarization?

Depolarization occurs when the membrane potential becomes less negative or moves toward a positive value.

What is the consequence of sufficient depolarization?

If a neuron is depolarized enough to reach a certain threshold, it will generate an action potential.

Define the Absolute Refractory Period.

A brief period immediately following an action potential during which it is virtually impossible for the neuron to fire another spike.

What does the firing rate r(t) represent?

Firing rate refers to the probability density of a spike occurring at a specific time t.

How is the Spike-Count Rate calculated?

It is calculated by taking the total number of action potentials in a trial and dividing it by the duration of the trial.

What is the main difference between firing rate and spike-count rate?

Firing rate is a temporal probability density, while spike-count rate is a time-averaged measure of spikes.

What does Spike-Triggered Averaging (STA) identify?

STA helps characterize neuronal selectivity by averaging the stimulus features present just before each spike occurrences.

What are Tuning Curves?

Tuning curves represent the average firing rate of a neuron measured against specific parameters of a stimulus.

What parameters might a Tuning Curve measure?

They often measure parameters like orientation (in vision), frequency (in hearing), or spatial position.

What is Weber's Law?

Weber's law states that the just noticeable difference (JND) in stimulus intensity is proportional to the original magnitude of the stimulus.

What is a 'Just Noticeable Difference' (JND)?

The smallest change in stimulus intensity that can be perceived or detected by the system.

Define a Poisson Process in the context of neural firing.

A statistical model where spike timings are independent and distributed randomly over time based on a constant firing rate.

What is the Fano Factor?

The Fano factor is the ratio between the variance of spike counts and the mean of spike counts (\text{Variance} / \text{Mean}).

What does a Fano Factor of 1 indicate?

A Fano Factor of 1 indicates that the spike-train variability matches a Poisson process.

What is the purpose of analyzing Spike-Train Statistics?

Analysts use these statistics to quantify the relationship between external stimuli and the variability in neural responses.

Define Neural Populations.

Neural populations are groups of multiple neurons working together collectively to encode or transmit information.

What is the significance of correlations in Neural Populations?

Correlations between the firing of different neurons can carry information that is not present in individual neuron firing rates.

How long is the typical duration of an action potential?

Approximately 1 ms.

What is the typical magnitude of the voltage change during a spike?

Approximately 100 mV.

What is a 'trial' in neural encoding experiments?

A single discrete interval during which a stimulus is presented and neural data is recorded.

What happens if a neuron is NOT sufficiently depolarized?

No action potential will be generated; the membrane potential may simply return to its resting level.

What does selectivity refer to in a neuron?

Selectivity refers to a neuron's preference for specific features of a stimulus, firing more intensely for some than others.

In terms of Weber's Law, if stimulus magnitude increases, what happens to the JND?

The just noticeable difference also increases, staying proportional to the magnitude.

What are 'Temporal Patterns'?

The specific arrangement of spikes in time, which can include the frequency, rhythm, and exact timing of events.

What does the mapping of stimulus to response mean?

It means creating a catalog or model that predicts how different inputs (stimuli) result in different outputs (neural spiking).

Is the absolute refractory period long or short?

It is very short, often occurring right after the peak of an action potential.

Why is the spike-count rate often averaged over several trials?

Averaging over trials helps account for the inherent variability in neural responses (spike-train statistics).

What is the relationship between the Fano factor and spiking variability?

A higher Fano factor indicates higher variability in the number of spikes produced across trials.

How do ion channels affect depolarization?

When certain channels open, positive ions flow into the cell, reducing the negative potential and causing depolarization.

What is the unit used to measure membrane potential in neurons?

Millivolts (mV).

What is the unit used to measure the duration of spikes?

Milliseconds (ms).

Can an action potential happen while an ion channel is in an absolute refractory state?

No, it is virtually impossible to initiate another spike during the absolute refractory period.

What is a temporal pattern?

A specific sequence or timing of spikes that the brain uses to interpret and carry information.