SLH 350 Test 2 Study Guide

Which is the preferred term/concept: sensitive period or critical period?

sensitive period

Sensitive period

plasticity is elevated early in life but doesn’t shut off at a hard boundary

Different aspects of language (phonology vs. vocabulary vs. syntax) may show…

different sensitivity windows rather than one uniform cutoff.

Sensitive period theory states that…

plasticity is elevated early in life but fades gradually, not a strict cutoff.

Synaptic/Functional Plasticity

strengthening or weakening of existing synaptic connections

Synaptic/Functional Plasticity changes often rely on

modifying the number of sensitivity of neurotransmitter receptors on the post synaptic cell

Structural plasticity

physically changes anatomical structure through creation of new synapses, dendritic growth

Left hemisphere stroke in language areas can lead to…

aphasia

In some stroke cases during recovery, the

perilesional cortex and sometimes the right hemisphere reorganize to take over lost function

This reorganization after a stroke is not:

neuron regeneration and not fixed purely by genetic

This reorganization after a stroke relies on

strong connection in the corpus callosum

this reorganization after a stroke shows that

plasticity persists in adults

Adults show neuroplasticity for non-native speech sounds…

in the auditory brainstem after long-term training

Plasticity is not just…

a developmental phenomenon, it operates across the lifespan

The earlier the age of L2 acquisition, the

greater cortical thickness/gray matter in language and cognitive control regions

Bilingual word-finding slips reflect

phonological interference between the two languages' sound systems.

phonological interference

saying a phonologically related word instead of the target one - “reach” instead of “peach”

phonological interference can also occur

across languages

semantic interference

words in both languages belonging to same category—saying a semantically related word instead of the target one

Invasive Electrophysiology

Invasively record from neurons using an electrode - requires some kind of surgery

Invasive electrophysiology is usually only done in animals or

in very limited circumstances on people (ex: in tissue that will later be resected in a surgery)

Invasive electrophysiology records

action potentials! Can measure either cell voltage or currents flowing through the cell

single unit electrophysiology

mesures action potential of ONE neuron

multi-unit electrophysiology

measures action potential of more than one (approx. 10) neurons at a time

Invasive electrophysiology has ______ spatial, ______ temporal

high, high

ECoG

electrocorticography

ECoG procedure

A grid of electrodes is placed on the surface of the brain to localize seizures in people with drug resistant epilepsy

In ECoG, each electrode records

100-1000s of neurons near that electrode, this signal is called the local field potential (LFP)

Is ECoG invasive?

yes, the electrodes are surgically placed on the cortical surface

ECoG has ____ spatial and ____ temporal

excellent, excellent

EEG

electroencephalography

What does EEG measure?

postsynaptic currents that reach the surface of the scalp in the form of voltage changes and magnetic fields

The voltage changes detected by EEG are generated by

approx. 500k to 1 million neurons

How is EEG recorded?

non-invasive scalp electrodes that are stuck to your scalp

EEG spatial resolution is

poor

EEG temporal resolution is

excellent - you can look at things happening at the millisecond level

MEG

magnetoencephalography

MEG measures

tiny magnetic fields generated by neuron’s electrical currents

MEG is especially sensitive to

sulci sources, but not gyri

Why is MEG sensitive to sulci, but not gyri sources?

this is due to the orientation of magnetic fields relative to tangential currents (physics of the magnetic field)

MEG has _____ temporal resolution, _____ spatial resolution

high, medium

Is MEG invasive?

no, it is non-invasive

Why does MEG have better spatial resolution than EEG?

the skull doesn’t distort or blur magnetic fields

fMRI

functional magnetic resonance imaging

fMRI looks at

brain activity over time

a structural MRI looks at

anatomy and pathology of the brain

Is fMRI invasive?

no

Unlike EEG, MEG, intracranial neurophysiology, fMRI does NOT measure

electrical activity or magnetic fields

fMRI does not directly measure

neural activity

fMRI uses BOLD, which allows us to

figure out which brain areas are most active

Oxyhemoglobin (HbO+) and deoxyhemoglobin (HbO-) have

different magnetic properties

BOLD: resting brain tissue has

normal mixture of HbO+ and HbO-; LOW signal in fMRI

Active brain tissue calls for extra blood, which causes

big rush of HbO+, upsetting the ratio of HbO+ and HbO-

When the ratio of HbO+ and HbO- is upset, there is a

HIGH signal in fMRI

What does BOLD stand for?

blood-oxygen-level dependent

Advantages of fMRI

• good spatial res

• inherently 3D

• measures the whole brain

disadvantages of fMRI

• very expensive and complicated

• poor temporal res

• does not measure neural activity directly

• cannot have metal in your body

fMRI contrast method step 1

subtract fMRI signal in one condition from fMRI signal in one condition from fMRI signal in other condition

fMRI contrast method step 2

use a statistical test to determine whether difference between conditions is significant

Contrast method can be used to

localize effects of interest (where they are in the brain)

fMRI science alternative approach

use natural stimuli (ex: a story) instead of controlled experiments, then build models that predict BOLD responses to new stimuli

fMRI has _____ spatial res and _____ temporal res

excellent, poor

fNIRS

functional near infrared spectroscopy

fNIRS measures

BOLD signal (like fMRI)

fNIRS uses _______, instead of huge magnets like fMRI uses

light emitters and detectors

fNIRS sends near infrared light from

emitter to detector

In fNIRS, the amount of diffused reflected light depends on

activity in underlying tissue

Oxygenated hemoglobin (HbO+) and deoxyhemoglobin (HbO-) absorb light at

different wavelengths

Why use fNIRS?

• non-invasive

• cost-effective

• portable

fNIRS can measure

oxygenated hemoglobin and de-oxygenated hemoglobin

fNRIS can be analyzed through

evoked (task-related data) and resting

fNIRS has _____ temporal res, and _____ spatial res

low, low

Other pros of fNRIS

movement-tolerant and you can have metal in your body!

fNIRS detects

hemodynamic changes via light

TMS

transcranial magnetic stimulation

Is TMS invasive?

no

TMS uses magnetic fields to

stimulate nerve cells in the brain

In TMS, electromagnetic coil is placed against the scale, sending

magnetic pulses throughout the skull that create time electrical signals that “wake up” underactive neurons or calm overactive ones

TMS is used to

target specific brain regions

TMS mechanism of action

1. coil generates magnetic field

2. this induces a localized electric current in the cortical tissue, which causes depolarization

TMS clinical uses

treats depression (and other psychiatric conditions) and primary progressive aphasia

TMS clinical use to the dorsolateral prefrontal cortex

improved action naming in PPA

TMS summary

magnetic induction causes neurons to depolarize

• casual method “virtual lesion” tool

tACS and tDCS

transcranial electrical stimulation

Direct current is

tDCS

alternating current is

tACS

tDCS mechanism of action

a weak, constant direct current is delivered through scalp electrodes (non invasive)

The tDCS current does not

directly trigger neuron firing, instead it subtly shifts the resting membrane potential of underlying neurons making them more or less likely to fire

tDCS polarity dependent effects of anodal stimulation

generally excitatory - depolarizing, shifting neurons closer to threshold (approx. -70 mV to +55 mV)

tDCS polarity dependent effects cathodal stimulation

generally inhibitory (hyperpolarizing)

tDCS summary

constant current, shifts overall excitability (anodal = excitatory, cathodal = inhibitory)

tDCS is similar to a ______ switch

dimmer

Is tDCS a casual method?

yes

tACS mechanism of action

an oscillating (alternating) current is delivered at a specific target frequency

tACS mechanism is designed to entrain or synchronize ongoing

neural oscillations to that frequency, not just simply exciting or inhibiting neuronal firing

tACS summary

oscillating current, entrains the TIMING of neural oscillations

tACS entrains the timing of neural oscillations, not

excitability level

is tACS a casual method?

yes

tDCS =

level of excitability (Can we shift excitability to help/hurt a task?)

tACS =

timing/rhythm (Can we casually confirm an oscillation’s timing matters?)