SLHS 50100 Test 1

Neural Bases of Speech and Language (*chapter study questions)

Chapter 1: The Human Brain

How many neurons does the human brain contain?\*

About 86 billion

What are the four principles of the neuron doctrine from Santiago Ramón y Cajal?

1. Neurons (“the butterflies of the soul”) are the basic signaling unit of the brain
2. They communicate only at specialized regions called synapses
3. They communicate only with certain other neurons
4. Within neurons, signals travel only in one direction

Soma

Cell body

Dendrites

Tree-like branches that receive signals from many other cells

Axon

A single long segment that splits toward the end to transmit signals to many other cells

Myelin sheath

Fatty substance that insulates the axon to facilitate signal propagation

Nodes of Ranvier

Gaps between myelin sheaths that enable the signal to be rejuvenated

Terminal buttons

Axon endpoints where neurotransmitters are released

Passive conduction

Dendritic inputs propagate freely to the soma of the neuron

Signal summation

If the combined dendritic inputs from all the pre-synaptic cells are large enough, an action potential will be initiated at the base (hillock) of the axon

Action potential

An electrical current that travels down the axon

Active conduction

Repeated renewal of a long-range electrical signal along the axon

Synapse

A small gap between an axon and a dendrite; neurotransmitters flow across it

How does an action potential/spike occur?\*

\-Default resting site: ions (electrically charged molecules) inside and outside the membrane of a neuron is -70 millivolts (mV) - more negative inside than outside

\-Dendritic input is strong enough to raise the inner potential to about -50 mV

\-Gates in membrane are opened and allow sodium (Na+) to rush in

\-Electrical balance reverses (becomes more positive inside than outside)

\-Sodium gates close and other gates open up

\-Potassium (K+) is pumped out of the cell so the current inside returns to negative

What type of affair is an action potential?

All-or-nothing; never a matter of degree

What does the action potential move progressively down?

The length of the axon

Where does the action potential move passively?

Myelin sheaths; they block the normal Na+/K+ transfer

Where is the action potential actively renewed?

Nodes of Ranvier; they allow the normal Na+/K+ transfer

What’s the most notable pathology where the destruction of myelin sheath occurs?

MS

What happens at terminal buttons?

\-Electrical impulses are converted to chemical neurotransmitters that cross the synaptic cleft

\-Signals are then converted back to electrical impulses in the dendrite of the post-synaptic cleft

What are the types of neurotransmitters?

Excitatory and inhibitory

How do neurons represent things?

By their firing frequency (how fast they fire)

Veins

Carry deoxygenated blood back to the heart

Hierarchical representation

Neurons that represent elementary features project to multiple layers of higher-order “conjunctive neurons” that represent increasingly complex stimuli

Neural landscape planes

\-Anterior: front

\-Posterior: back

\-Dorsal: superior

\-Ventral: inferior

Axial slice

Looking at the brain from the top and bottom

Coronal slice

Looking at the brain front and back

Sagittal slice

Looking at the brain left and right

Brainstem\*

\-Top of the spinal cord

\-Three components: midbrain, pons, and medulla

\-**Homeostasis** (heart rate, blood pressure, breathing, coughing, vomiting, digestion, reward/pleasure, consciousness, etc.)

\-Houses cranial nerves that receive sensory input from, and send motor output to, the head and neck

Thalamus\*

\-**”Gateway to the cortex”**

\-Egg-shaped structures that’s on top of the brainstem

\-Has reciprocal (bidirectional) connections with all regions of the cortex

Why is the thalamus called the “gateway to the cortex”?

All sensory inputs (except smell) pass through it before reaching the cortex

What do the thalamus cortex loops facilitate?

Attention, short-term memory, and the coordination of widely distributed cortical areas

Hippocampus\*

\-**Memory consolidation**

\-Sausage-shaped structure in the medial temporal lobe

\-Receives a huge amount of highly processed input from the temporal and parietal lobes

What are the two traditional views of the hippocampus’ function?

1. Spatial navigation
2. Episodic memory

What type of organization does the hippocampus do in terms of abstract domains?

\-Larger in London taxi drivers, piano tuners, and medical students

\-Map of social space that represents people at different distances along dimensions like power and affiliation

\-Tracks the distances between word meanings in semantic memory

Amygdala\*

\-**Regulate emotion**

\-Almond-shaped structure in the medial temporal lobe

\-Central role in representing the current value of stimuli

\-Process emotionally and socially relevant information, including negative or potentially threatening facial expressions

\-Fear conditioning

What happened to a patient whose amygdala didn’t develop normally?

\-Impaired recognition of fearful faces

\-Doesn’t experience fear themself

Basal ganglia\*

\-Set of nuclei beneath the frontal and temporal lobes

\-Receive massive inputs from the entire cortex, route those signals through two parallel pathways (“go” and “no-go”), and send the output to the frontal lobes via the thalamus

\-Acquisition, selection, initiation, and cessation of adaptive (rewarding) vs. maladaptive (non-rewarding) thoughts and behaviors **(motor control)**

What are the names of the basal ganglia nuclei? (7)

\-Putamen

\-Global pallidus (lateral part)

\-Global pallidus (medial part)

\-Caudate nucleus

\-Thalamus

\-Subthalamic nucleus

\-Substantia nigra

What pathological conditions is the basal ganglia dysfunctional in?

\-Parkinson’s disease

\-Huntington’s disease

\-Tourette’s syndrome

\-OCD

\-Schizophrenia

Cerebellum\*

\-Space behind the medulla and pons

\-”Little brain”

\-Contains nearly 70 billion neurons

\-Regulates muscle tone and ensures movements are executed fluidly (time and coordination)

\-Cognition

What are the four visible lobes of the cerebral cortex? One hidden lobe?

Visible lobes

\-Frontal (reasoning, motor control, emotion, language)

\-Parietal (processing information from the body’s senses, somatosensory)

\-Temporal (hearing)

\-Occipital (vision)

\
Hidden lobe

\-Insula

Gray matter vs. white matter

\-Gray: made up of cell bodies, not heavily myelinated

\-White: made up of nerve fibers, heavily myelinated

Gyri (singular = gyrus)

Raised bulges

Sulci (singular = sulcus)

Deep grooves

Planum temporale

Higher order speech

Cytoarchitectonic organization

Similarities and differences between cortical areas with respect to the distribution, density, size, and shape of neurons

How does the cytoarchitectonic organization of the cerebral cortex differ from its gyral/sulcal organization?

\-There are many discontinuities marked by shifts in the thickness and composition of the six tiers/layers

\-Parcellation schemes vary substantially in the precise number and configuration of cortical areas

Brodmann areas (BAs)

Mostly cross-cut gyral/sulcal borders, and for the most part they should be treated as structurally rather than functionally defined regions

What are the Brodmann areas based on?

Cytoarchitecture (varies across cortical surfaces)

Corpus collosum

The biggest and busiest white matter fiber tract

Fasciculi (singular = fasciculus)

White matter fiber tracts that interconnect different cortical areas within the same hemisphere (e.g. arcuate fasciculus)

Which fasciculi (i.e., long-distance fiber tracts) in the left hemisphere have been associated with language? How many segments is it?\*

\-Arcuate fasciculus

\-3

What will give you an aphasia?

Damage to the white matter segments

What are the two classic language-related regions of the left hemisphere?

1. Broca’s area
2. Wernicke’s area

Broca’s area

\-Frontal

\-Originally thought to be mainly for production

Wernicke’s area

\-Posterior superior temporal

\-Originally thought to be mainly for comprehension

Why are the two classic language-related brain regions – Broca’s area and Wernicke’s area – problematic?\*

There is no agreement on the anatomical boundaries of either region

Chapter 2: Brain Mapping Methods

What are the four main methods for investigating the neural substrates of linguistic abilities?

\-Neuropsychology

\-Functional neuroimaging (PET and fMRI)

\-Electrophysiology

\-Transcranial magnetic stimulation (TMS)

What’s the oldest method in cognitive neuroscience?

Neuropsychology

Single dissociation\*

\-Patient A performs significantly worse on task X than on task Y

\-Suggests that lesion has selectively disrupted some mental representations and/or computations that are required by task X but not by task Y (possible conclusion)

\-However, task X may just be a lot harder than task Y, and the lesion may have induced greater sensitivity to this difference in difficulty

Double dissociation\*

\-Patient A performs significantly worse on task X than on task Y, and patient B performs significantly worse on task Y than on task X

\-Reduces the likelihood that either patient’s performance may be due to differences in task difficulty

\-**Supports the view that each task requires at least some mental representations and/or computations that can be selectively disrupted**

Stroke

The blood supply to a particular part of the brain is cut off, depriving the down-stream tissue of oxygen

Thrombotic stroke

A clot forms within the blood vessel and eventually clogs it

Embolic stroke

A clot forms in some other part of the circulatory system, and when it travels up into the brain it eventually gets stuck in an artery

What happens if blood flow isn’t restored quickly?

The tissue dies and it leaves a cavity that gets filled with CSF

Traumatic Brain Injury (TBI): Closed head

A person sustains a sudden blow to the head that damages the brain while leaving the skull intact (car or sporting accident)

Traumatic Brain Injury (TBI): Open head

Both the brain and the skull are penetrated by an object such a a bullet or a piece of shrapnel

Neurodegenerative and infectious diseases

Progressive in nature and involve atrophy (gradual tissue loss) in specific regions, or sets of regions, of the brain

Alzheimer’s

\-Type: degenerative

\-Affected brain regions: medial temporal areas, lateral temporoparietal areas, posterior cingulate/precuneus

Parkinson’s

\-Type: degenerative

\-Affected brain regions: dopaminergic cells in substantia nigra

Huntingon’s

\-Type: degenerative

\-Affected brain regions: caudate and putamen in basal ganglia

Corticobasal syndrome

\-Type: degenerative

\-Affected brain regions: primary and higher-order sensorimotor cortices in frontoparietal regions

Amyotrophic lateral sclerosis

\-Type: degenerative

\-Affected brain regions: motor neurons

Multiple sclerosis

\-Type: possibly infectious

\-Affected brain regions: demyelination, especially of fibers near ventricles

Herpes simplex encephalitis

\-Type: infectious

\-Affected brain regions: ventral, medial, and polar temporal areas: amygdala, hippocampus, insula, anterior cingulate

Nonfluent/grammatic variant PPA

\-Type: degenerative

\-Affected brain regions: inferior frontal cortex (left)

Semantic variant PPA

\-Type: degenerative

\-Affected brain regions: anterior temporal lobes

Logopenic variant PPA

\-Type: degenerative

\-Affected brain regions: superior temporal and inferior parietal areas (left)

What are the three different distributions of significant cortical thinning in the three variants of primary progressive aphasia (PPA)?

\-Nonfluent progressive aphasia (NFPA)

\-Semantic dementia (SD)

\-Logopenic progressive aphasia (LPA)

NFPA

Cortex is significantly thinner than in a normal control group

SD

A lot of trouble with the meaning of words

LPA

\-Left temporal parietal

\-Word finding difficulties

\-Phonological problems

Tumors

Masses of tissue that grow abnormally and serve no physiological purpose

Lesion overlap and subtraction analysis

1. First, two groups of brain-damaged patients are recruited: one with the deficit of interest, and another without it
2. Second, for each group, the contours of the patients’ lesions are reconstructed on a standard brain template, and the degree to which they overlap is calculated at every voxel.  (A voxel is a 3D volume element usually measured in millimeters)
3. Third, the lesion overlap map for the patients without the deficit is subtracted from the one for the patients with the deficit, in order to pinpoint the areas of damage associated specifically with the deficit

Voxel-Based Lesion-Symptom Mapping (VLSM)\*

\-Go voxel by voxel and see who had damage there/who didn’t and did they perform differently on the task

\-Find where voxels did damage performance

Voxel-Base Morphometry (VBM)\*

\-Neurodegenerative diseases

\-Where are there voxels that correlate with the degree of impairment on a task

What are the four caveats about neuropsychological research on structure-function relationships?

1. All three of the approaches just described have statistical shortcomings
2. Structure-function relationships may re-organize after brain damage
3. Some impairments may be due to a disconnection between regions
4. Some impairments may be due to reduced blood flow (hypoperfusion) in certain regions

What do PET and fMRI measure in different ways?\*

Regional changes in blood flow associated with neural activity

fMRI\*

\-Measures the “blood oxygenation level dependent” (BOLD) signal, which decreases when blood is deoxygenated and increases when blood is oxygenated

\-The “hemodynamic response function” (HRF) shows how the BOLD signal evolves over time:

* Initial dip, as immediately available oxygen is consumed (about 1‒2 seconds)
* Steady rise, as freshly oxygenated blood is delivered (about 5 seconds)
* Gradual drop, as the signal returns to baseline (about 5 seconds)

\-Spatial resolution = 3 mm or less (depends on magnet);  temporal resolution = even shorter than the HRF, and getting better all the time (sub-second range)

What’s the difference between single-cell recording and electrocorticography?\*

\-Single-cell recording: can reveal the unique response properties of particular neurons

\-Electrocorticography: local field potentials recorded from electrode grids placed directly over the cortex which allows this form of data acquisition and analysis

Which brain mapping methods allow researchers to determine whether a particular region is actually necessary for a particular ability?\*

fMRI

Block design

Stimuli from the same condition are presented consecutively together (required for PET, optional for fMRI)

Event-related design

Stimuli from one condition are randomly interspersed with stimuli from another condition (impossible for PET but possible/preferred for fMRI)

Why might event-related design be preferred over block design?

\-Participants can’t predict what stimulus they’ll get next so they are less likely to slip into a habitual pattern of responding

\-You may only want to analyze data from when your participant gave a correct response

Subtraction paradigm (simple version)\*

Two conditions:

\-Experimental (A): requires ability of interest

\-Control (B): doesn’t require that ability, but is equivalent in other ways

\
\-Contrast the activation map for the experimental condition (A) against the one for the control condition (B) to reveal the brain areas unique to the ability of interest

Correlation/Parametric paradigm\*

\-Ability of interest is a continuous cognitive dimension that can be manifested to varying degrees

\-Subjects perform tasks that recruit the ability of interest to different extents, and the investigators look for brain regions in which the magnitude of activity shifts accordingly

Multivariate Pattern Analysis (MVPA)\*

\-Extracts the information contained in the patterns of activity across voxels

\-Can reveal whether two (or more) conditions can be distinguished from each other on the basis of the activity patterns in a set of voxels