Chapter 2

Question 1

Neurons

Answer 1

The structure that transmits electrical signals in the body. Key components of neurons are the cell body, dendrites, and the axon or nerve fiber.

Question 2

Neuron cell body

Answer 2

The part of a neuron that contains the neuron’s metabolic machinery and that receives stimulation from other neurons.

Question 3

Dendrites

Answer 3

Nerve processes on the cell body that receive stimulation from other neurons.

Question 4

Axon

Answer 4

The long part of the neuron filled with fluid that conducts nerve (electrical) impulses over distances. Also called the nerve fiber. There are variations on this basic neuron structure: Some neurons have long axons; others have short axons or none at all.

Question 5

Sensory receptors

Answer 5

Neurons specialized to respond to environmental stimuli.

Question 6

How to study electrical signals in perception research?

Answer 6

Record signals from single neurons, which provides valuable information about what is happening in the nervous system. Still, it’s important to record from as many neurons as possible, because different neurons may respond differently to a particular stimulus or situation.

Question 7

Resting potential

Answer 7

The difference in charge between the inside and the outside of the nerve fiber when the fiber is not conducting electrical signals. Most nerve fibers have resting potentials of about 270 mV, which means the inside of the fiber is negative relative to the outside

Question 8

Action potential

Answer 8

Rapid increase in positive charge in a nerve fiber that travels down the fiber. Also called the nerve impulse. It lasts about 1 millisecond. It is indentified by the predictable rise and fall of the charge inside the axon relative to the outside (from -70mV to +40mV and back to -70mV).

Question 9

Properties of the Action Potential

Answer 9

• The AP (propagated response) travels all the way down the nerve fiber without decreasing in amplitude.
• The AP remains the same size no matter how intense the stimulus is. Changing the stimulus intensity does not affect the size of the action potentials but does affect the rate of firing (within limits of refractory period)

Question 10

Refractory period

Answer 10

The time period (another millisecond) that a nerve fiber needs to recover from conducting a nerve impulse. No new nerve impulses can be generated in the fiber until the refractory period is over. Although increasing the stimulus intensity can increase the rate of firing, there is an upper limit to the number of nerve impulses per second that can be conducted down an axon because of this period (around 500-800 impulses per second at maximum).

Question 11

Spontaneous activity

Answer 11

Nerve firing that occurs in the absence of environmental stimulation. This establishes a baseline level of firing for the neuron. The presence of stimulation usually causes an increase in activity above this spontaneous level, but under some conditions, it can cause firing to decrease below the spontaneous level.

Question 12

Ions

Answer 12

Charged molecules. Ions are created when molecules gain or lose electrons, as happens when compounds are dissolved in water. Sodium (Na+), potassium (K+), and chlorine (Cl-) are the main ions found within nerve fibers and in the liquid that surrounds nerve fibers. This distribution of ions across the neuron’s membrane is important to maintaining the −70 mV resting potential, and for the initiation of the AP.

Question 13

Ions during the AP

Answer 13

As an action potential begins traveling down the axon, positively charged sodium ions rush into the axon. This occurs because channels in the membrane that are selective to Na+ have opened. The inflow of positively charged sodium causes an increase in the positive charge inside the axon from the resting potential of −70 mV until it reaches the peak of the action potential of +40 mV. Once it does, the sodium channels close and potassium channels open. Because there were more potassium ions inside than outside the neuron while at rest, positively charged potassium rushes out of the axon when the channels open, causing the charge inside the axon to become more negative.

Question 14

Membrane permeability

Answer 14

A property of a membrane that refers to the ability of molecules to pass through it. If the permeability to a molecule is high, the molecule can easily pass through the membrane.

Question 15

Depolarization

Answer 15

When the inside of a neuron becomes more positive, as occurs during the initial phases of the action potential. Depolarization is often associated with the action of excitatory neurotransmitters.

Question 16

Rising phase of the action potential

Answer 16

In the axon, the decrease in negativity from -70 mV to +40 mV (the peak action potential level) that occurs during the action potential. This increase is caused by an inflow of Na+ into the axon.

Question 17

Hyperpolarization

Answer 17

When the inside of a neuron becomes more negative. Hyperpolarization is often associated with the action of inhibitory neurotransmitters.

Question 18

Falling phase of the action potential

Answer 18

In the axon, or nerve fiber, the increase in negativity from +40 mV back to -70 mV (the resting potential level) that occurs during the action potential. This increase in negativity is associated with the flow of positively charged potassium ions (K+) out of the axon. Once the membrane potential is back to -70mV, the K+ flow stops.

Question 19

Sodium-potassium pump

Answer 19

A mechanism that keeps sodium from building up inside the axon and potassium from building up outside, by continuously pumping sodium out and potassium into the cell.

Question 20

Synapse

Answer 20

A small space between the end of one neuron (the presynaptic neuron) and the cell body of another neuron (the postsynaptic neuron).

Question 21

Neurotransmitters

Answer 21

A chemical stored in synaptic vesicles that is released in response to a nerve impulse and has an excitatory or inhibitory effect on another neuron.

Question 22

Receptor sites

Answer 22

Small area on the postsynaptic neuron that is sensitive to specific NTs. These receptor sites exist in a variety of shapes that match the shapes of particular NT molecules. When a NT makes contact with a receptor site matching its shape, it activates the receptor site and triggers a voltage change in the receiving neuron.

Question 23

Excitatory response

Answer 23

The response of a nerve fiber in which the firing rate increases. It occurs when the neuron becomes depolarized, and thus the inside of the neuron becomes more positive. To generate an action potential, enough excitation must occur to increase depolarization to the needed level (ex. -65mV). It might take more than one excitatory response (such as what occurs when multiple NTs from a number of incoming neurons all reach the receptor sites of the receiving neuron at once) to trigger an AP.

Question 24

Inhibitory response

Answer 24

Occurs when a neuron’s firing rate decreases due to inhibition from another neuron. Hyperpolarization is an inhibitory response because it causes the charge inside the axon to move away from the level of depolarization needed to generate an AP. Since a typical neuron receives both excitation and inhibition, the response of the neuron is determined by the interplay of excitation and inhibition.

Question 25

Sensory coding

Answer 25

How neurons represent various characteristics of the environment.

Question 26

Specificity coding

Answer 26

Type of neural code in which different perceptions are signaled by activity in specific neurons. This idea that one neuron can represent one stimulus or concept, such as a face, dates back to the 1960s. At that time, Jerome Lettvin proposed the idea that neurons could be so specific that there could be one neuron in your brain that fires only in response to, say, your grandmother.

Question 27

The grandmother cell

Answer 27

A highly specific type of neuron that fires in response to a specific stimulus, such as a person’s grandmother. This term was coined by Lettvin. According to him, even just thinking about the idea of your grandmother could make your grandmother cell fire. Along this reasoning, you would also have a “grandmother cell” for every face, stimulus, and concept that you’ve ever encountered.

Question 28

Evidence for specificity coding

Answer 28

In the early 2000s, Quiroga recorded from the temporal lobe of patients undergoing brain surgery for epilepsy. These patients were presented with pictures of famous people from different viewpoints, in order to see how the neurons responded. Some neurons responded to a number of different views of just one person, or to a number of ways of representing that person. Thus, these neurons were not just responding to the visual input of the famous person’s face, but also to the concept of that particular person.

Question 29

Problems with the grandmother cell idea

Answer 29

While the finding of Quiroga’s study does seem consistent with the idea of grandmother cells, it does not prove that they exist. In fact, the researchers themselves think they didn’t have enough time to properly study the neurons individually (and if they had more, maybe they’d have found that several faces would have made the same neuron fire). The idea of grandmother cells is not typically accepted by neuroscientists today, given the lack of confirmatory evidence and its biological implausibility (it would require more neurons that we have, and the creation of new neurons everytime we encounter something new).

Question 30

Sparse coding

Answer 30

The idea that a particular object is represented by the firing of a relatively small number of neurons (a specific stimulus activates a specific pattern of neurons). It was proposed by Quiroga himself to explain his results. There is biological evidence for this theory.

Question 31

Population coding

Answer 31

Representation of a particular object or quality by the pattern of firing of a large number of neurons. An advantage of population coding is that a large number of stimuli can be represented, because large groups of neurons can create a huge number of different patterns. There is good evidence for population coding in each of the senses, and for other cognitive functions as well.

Question 32

Phrenology

Answer 32

Introduced by German physiologist Gall in the 18th century, who observed a correlation between the shape of a person’s skull and their abilities and traits (“mental faculties”). Based on his observations, Gall concluded that there were about 35 different mental faculties that could be mapped onto different brain areas based on the bumps and contours on the person’s skull. Although phrenology has now been debunked as a method, it was the first proposal that different functions map onto different areas of the brain - a concept that is still discussed today.

Question 33

Modularity

Answer 33

The idea that specific areas of the cortex (modules) are specialized to respond to specific types of stimuli. Early evidence supporting modularity of function came from case studies of humans with brain damage.

Question 34

Module

Answer 34

A structure that processes information about a specific behavior or perceptual quality. Often identified as a structure that contains a large proportion of neurons that respond selectively to a particular quality, such as the fusiform face area, which contains many neurons that respond selectively to faces.

Question 35

Broca’s area

Answer 35

An area in the frontal lobe that is important for language perception and production. One effect of damage is difficulty in speaking. Discovered by Broca, a physician studying people with brain damage (19th century)

Question 36

Wernicke’s area

Answer 36

An area in the temporal lobe involved in speech perception. Damage to this area causes Wernicke’s aphasia, which is characterized by difficulty in understanding speech. Identified by Wernicke (19th century)

Question 37

Neuropsychology

Answer 37

The study of the behavioral effects of brain damage in humans.

Question 38

Brain imaging

Answer 38

Procedures that make it possible to visualize areas of the human brain that are activated by different types of stimuli, tasks, or behaviors. The most common technique used in perception research is functional magnetic resonance imaging (f MRI).

Question 39

MRI

Answer 39

Magnetic Resonance Imaging: a brain scanning technique that makes it possible to create images of structures within the brain. Invented in the 1980s, and used since then to detect brain abnormalities such as tumors.

Question 40

fMRI

Answer 40

A brain imaging technique that indicates brain activity in awake, behaving organisms. The fMRI response occurs when the response to a magnetic field changes in response to changes in blood flow in the brain. fMRI is limited in that it can’t record activity from individual neurons. Instead, what’s being recorded is activity in subdivisions of the brain called voxels, which are small cube-shaped areas of the brain about 2 or 3 mm on a side. Voxels are not brain structures but are simply small units of analysis created by the fMRI scanner.

Question 41

Mapping out the brain

Answer 41

Many researchers have used brain imaging techniques like fMRI in an attempt to map a certain function onto a specific area of the brain. For example, a 2000 study using fMRI showed that an area in the temporal lobe - the superior temporal sulcus - was activated significantly more in response to vocal sounds than non-vocal sounds. This area was therefore dubbed the “voice area” of the brain, given its highly specialized response. This supports a modular view of brain function.

Question 42

Distributed representation

Answer 42

Occurs when a stimulus causes neural activity in a number of different areas of the brain, so the activity is distributed across the brain. Idea presented by Hinton in 1986. One example of distributed representation is how the brain responds to pain: pain perception involves multiple components (sensory, emotional, reflexive…). These activate a number of structures distributed across the brain.

Question 43

Structural connectivity

Answer 43

The structural “road map” of fibers connecting different areas of the brain.

Question 44

Functional connectivity

Answer 44

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

Question 46

Types of fMRI

Answer 46

• Task-related fMRI: fMRI measured as a person is engaged in a specific task.
• Resting-state fMRI: The signal recorded using functional magnetic resonance imaging when the brain is not involved in a specific task.

Question 47

Seed location

Answer 47

Location on the brain that is involved in carrying out a specific task and which is used a reference point when measuring resting-state functional connectivity.

Question 48

Resting-state functional connectivity

Answer 48

A method in which resting-state fMRI is used to determine functional connectivity. Saying two areas are functionally connected does not necessarily mean that they directly communicate by neural pathways. For example, the response from two areas can be highly correlated because they are both receiving inputs from another area.

Question 49

Test location

Answer 49

Resting-state fMRI measured at a location other than the seed location.

Question 50

Steps of Resting-state functional connectivity

Answer 50

• Determine seed location
• Measure resting-state fMRI at seed location (time-series response: it indicates how the response changes over time)
• Measure test location
• Calculate correlation between seed and test location responses. Low correlation = poor/no functional connectivity

Question 51

Why measure functional connectivity?

Answer 51

It can be used to predict behavior. For example, researchers found that the strength of functional connectivity immediately before the detection task predicted how likely it was that the person would perceive a stimulus.

Question 52

The mind-body problem

Answer 52

One of the most famous problems in science: How do physical processes such as nerve impulses or sodium and potassium molecules flowing across membranes (the body part of the problem) become transformed into the richness of perceptual experience (the mind part of the problem)? Connections between electrical signals and perception are just correlations - they can’t explain what causes our subjective experience of perception.