Electrophysiology

Question 1

Spike sorting

Answer 1

attempts to isolate individual cells from background activity during single unit recording (filter out background noise)

Question 2

Spike train

Answer 2

• Output of unit recordings is often depicted as a spike train, and is measured in spikes/second
• Even without sensory input, spike rate is almost never zero
○ Most of the brain is active most of the time (even if not being stimulated)
i.e. Neuron that responds to the colour red will remain active (idling), but activity will spike is the colour red is presented

Question 3

EEG Oscillagtion

Answer 3

• EEG oscillations is an indicator of how brain areas “talk” to one another
○ Communication between brain areas occurs in synchronized waves going back and forth
○ Higher frequency= faster communication
Things like visual perception needs to be temporally precise, so has a high frequency

Question 4

Magnetoencephalography (MEG):

Answer 4

Good temporal, poor spatial resolution

Measures magnetic fields produced by electrical activity in the brain via extremely sensitive devices
• 102 location in the brain, each containing 3 sensors (306 total)
○ 2 planar gradiometers
○ 1 magnetometer
• Measured with SQUIDS (superconducting quantum interference devices
○ Measured at very cold temperatures because changes in magnetic fields due to brain activity are very subtle, needs to be cold to be detected

MEGs don’t measure polarities (positive or negative), instead, what is seen is changes in magnetic activity

Question 5

Electroencephalography (EEG)

Answer 5

Good temporal, poor spatial resolution

	○ Measurements of electrical signals generated by the brain through electrodes place on different points on the scalp Useful for measuring timing of cognitive events

Question 6

Local Representation

Answer 6

All info about a stimulus/event is carried in one of the neurons (i.e. a grandmother cell)

Question 7

Full Distributed Representation

Answer 7

All info about a stimulus/event is carried in all neurons of a given population

• Distributed representation may protect against information loss if synapses or neurons are lost
	○ Also allows cognitive system to generalize and categorize  i.e. a novel stimulus that resembles a stored representation would partially activate this representation

Question 8

Sparse Distributed Representation

Answer 8

§ Distributed representation in which a small proportion of the neurons carry info about a stimulus/event

• i.e. Several (but not all) neruons needed to represent a particular face

Studies are consistent with this theory

Sparseness coding conserves energy and may enable the brain to have a high memory capacity

Question 9

Rate Coding:

Answer 9

Stimulus/event is associated with an increase in rate of neural firing

Question 10

Temporal Firing:

Answer 10

• Given stimulus/event is associated with greater synchronization of firing across different neurons
• i.e. 2 regions stimulated with a single bar of light
○ Neural firing synchronized
• Stimulated by 2 different bars of light
No synchronization even though there was an increased rate of firing in both cells

Question 11

Additive Factors Methods

Answer 11

○ General method for dividing RT into different stages
§ Encoding
§ Comparing
§ Decision
§ Responding
Different factors can affect each stage, effects are additive

Question 12

Endogenous ERP Components

Answer 12

○ Depend on properties of task

Can occur in the absence of an external stimulus (i.e. if the expected stimulus does not occur

Question 13

Exogenous ERP Components

Answer 13

○ Appear to depend on the physical properties of a stimulus
○ i.e. size, sensory modality..etc
Also called evoked potentials