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

Endpoints of the axon where chemical 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

What’s the percentage of human brain that compromises body weight? Consumes oxygenated blood flowing from the heart?

\-2-3%

\-20%

Arteries

4-10 millimeters in diameter

Arterioles

20-50 micrometers in diameter

Capillaries

10 micrometers in diameter

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

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

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

\-”Gateway to the cortex”

\-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\*

\-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\*

\-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

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

\-Parietal

\-Temporal

\-Occipital

\
Hidden lobe

\-Insula

How many neurons does the cerebral cortex contain? How thick is it?

\-16 billion neurons

\-2-4 mm thick

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

Corpus collosum

The large white matter fiber tract that interconnects the two hemispheres

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?\*

Arcuate fasciculus

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

1. Broca’s area
2. Wernicke’s area

Broca’s area

Originally thought to be mainly for production

Wernicke’s area

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)

Which method dominates the field?

fMRI

What does neuropsychology involve?

Using behavioral and lesion data from brain-damaged patients to determine not only which mental abilities can be impaired independently of others, but also which neural structures are necessary to support them

What’s the oldest method in cognitive neuroscience?

Neuropsychology

What are the two general aims with regard to language?

\-To carve the language faculty at its joints by determining which of its components can be selectively disrupted (understand the cognitive architecture of language)

\-To identify reliable links between specific linguistic deficits and specific lesion sites (understand the neural architecture of language)

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

What are cases studies useful for?

\-Identifying unusual patterns of dissociation

\-Provide hints about deficit-lesion correlations

What are group studies useful for?

\-Testing the reliability of deficit-lesion correlations

Magnetic Resonance Imaging (MRI)

\-The protons in the hydrogen atoms of water molecules have randomly oriented spins

\-The scanner creates a large magnetic field that causes some of those protons to become aligned with it

\-A radio wave is then passed through the volume, causing the aligned protons to absorb some of this energy and shift their orientation by 90 degrees

\-When the radio wave is turned off, the protons release the energy as they “relax” back into alignment with the magnetic field of the scanner

\-This “relaxation” process generates the signals that are used to create brain images

\-Different tissues, like gray versus white matter, have different densities of hydrogen, and this leads to different relaxation rates of protons

\-The spatial resolution of brain scans can be less than 1 mm

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

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 an 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

What’s the most common type of tumor?

Gliomas

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)\*

\-Administer a task to a sample of patients with widely distributed lesions

At each voxel, form two groups of patients—one with damage at that location, and another without

Use *t*-tests to statistically compare the task performances of the two groups at each voxel and thereby determine where damage leads to impairment

Voxel-Base Morphometry (VBM)\*

\-Treated in a graded manner as having a variable amount of damage ranging from 100% to 0%

\-Ideal for studying patients with neurodegenerative diseases

\-Researchers can use VBM to discover correlations between performances on particular tasks and gray matter densities in particular cortical regions

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 are the two main techniques of functional neuroimaging?

PET and fMRI

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

Regional changes in blood flow associated with neural activity

PET

\-Tracks the distribution of a radioactive isotope (15O) through the brain

\-The locations of annihilation events are reconstructed by a computer

\-Where the number of such events is relatively large, there is greater blood flow, and where there is greater blood flow, there is greater neural activity

\-Spatial resolution = about 10 mm;  temporal resolution = about 30 seconds at best

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