Ch 2: Basic Principles of Sensory Processing

Neural processing

The interaction of the signals of many neurons

Electrical signals occur in structures called

Neurons

Cell body/ soma

Contains mechanisms to keep cell alive

Dendrites

Branch out from cell body to receive electrical signals from other neurons

Axon/ nerve fiber

Filled with fluid that conducts electrical signals

Sensory receptors

Neurons specialized to respond to environmental stimuli

Recording electrical signals in neurons

Recorded from the axons using small electrode to pick up the signals

Resting axon

Inside is 70mV more negative than outside (no signals in the neuron), resting potential

Action potential

Signal with rise + fall of the charge inside the axon relative to outside

(Neuron firing)

Propagated response

Once response is triggered, it travels all the way down the axon without decreasing in size

Size of response

Remains same size no matter how intense stimulus is

Does not affect size, but does affect the rate of firing

Refraction period

The interval between the time one nerve impulse occurs and the next one can be generated in the axon

Spontaneous activity

Action potentials that occur in absence of stimuli from environment establishes a baseline level of firing for the neuron

Neurons are bathed in a liquid solution rich in …

Ions

Outside the neuron is rich in

Na+

Inside the neuron is rich in …

K+

Chemical basis of action potential

Channels open, increase in permeability to sodium, Na+ rushes in

Permeability

Ease with which a molecule can pass through the membrane

Selective

The fibre is permeable to one specific type of molecule

Depolarization

-70 to +40 mV

(Rising phase of the action potential)

What happens when +40 is reached

Sodium channels close

Potassium channels open, rush out

Hyperpolarization

+40mV to -70mV

(Falling phase of the action potential)

Synapse

Very small space between neurons

Neurotransmitters

Chemicals released when AP reaches the end of a neuron

Where are neurotransmitters stored

In synaptic vesicles (at end of sending neuron)

Receptor sites

Small area on receiving neuron where the neurotransmitters flow into

Sensitive to specific neurotransmitters

(Matches, activates site, triggers voltage change in receiving neuron)

Excitatory response

Neuron becomes depolarized (inside becomes more positive)

Must be high enough to generate AP

Inhibitory response

Inside of neuron becomes more negative/ hyperpolarized (moving away from level for AP)

Processing info (rather than transmitting)

Sensory code

How neurons represent various characteristics of the environment

Specificity coding

Notion of a specialized neuron that responds only to one concept/ stimulus

(Ex grandmother cell → highly specific type of neuron that would respond only to your grandmother, not just visual input but also to the concept)

Not really accepted today

Spare coding

Occurs when a particular stimulus is represented by a pattern of firing of only a small group of neurons, with the majority of neurons remaining silent

Population coding

Proposes our experiences are represented by the patterns of firing across a large number of neurons

Sometimes groups are small, sometimes large

Phrenology

Idea that there are 35 different mental faculties that could be mapped onto different brain areas based on bumps/ contours on a person’s skull

(Ridge on the back of your head means you’re a loving person)

Debunked*

Modularity

Idea that specific brain areas (modules) are specialized to respond to specific types of stimuli or functions

Still relevant

Broca’s area

Speech production area of brain

Wernicke’s area

Area in temporal lobe involved in speech production

Neuropsychology

Field on the location of brain damage to specific effects on behaviour

Brain imaging

Records brain responses in neurologically normal humans

MRI (magnetic resonance imaging)

Creates images of structures within brain

fMRI

Determines how various types of cognition or functions activate different parts of the brain

Distributed Representation

Concept that the brain represents info in patterns distributed across the cortex, rather than in one single brain area

(Ex pain, each area serves a different aspect of pain perception)

Structural connectivity

The “roadmap” of fibres connecting different areas of the brain

(MRI, structure)

Functional connectivity

The neural activity associated with a particular function that is flowing through this structural network

(fMRI, function)

Task related fMRI

Measured as a person is engaging in a specific task

Resting state fMRI

Not involved in specific task, used to measure functional connectivity

Measuring resting state functional connectivity

1. Use task related fMRI to figure out brain location associated with specific task (seed location)

2. Measure resting state fMRI at seed location

3. Measure resting fMRI at another location (test location)

4. Calculate correlation between two locations

(measures how strongly different brain regions work together while a person is not performing a specific task)

Two areas can be functionally connected but

Don’t necessarily directly communicate by neural pathways

Mind Body Problem

How do physical processes like nerve impulses become transformed into the richness of the perceptual experience

How do physical processes cause our experiences