record neurons using electrode (usually wire or glass) and the ACTION POTENTIALS, can measure cell voltage or currents
Is electrophysiology invasive?
YES, usually requires some sort of surgery
What is electrophysiology usually done on?
Animal models (limited circumstances in people)
What are glass electrodes for?
intracellular recordings (ex: "patch clump")
Whole cell intracellular recordings
electrodes filled with solution, stuck into brain tissue until contact with cell, researcher sucks up plasma membrane and records action potentials from single neuron
Electrodes for extracellular electrophysiology
records multiple neurons at once from outside of the cell with a metal electrode (metal, or four wires twisted together)
very small; measures many neurons in a local area at once; was used to control a robotic arm (Brain Gate 2)
grid of electrodes placed on surface of the brain to localize seizures in people with drug resistant epilepsy
Why is ECoG helpful if stroke is lateralized?
ECoG sees which electrodes where first involved and where it spread, if the stroke were all over this wouldn't help.
What is local field potential (LFP)?
the signal recorded from 100s of neurons near an electrode
Is ECoG invasive?
What is used with ECoG to see where electrodes are?
CT scan and MRI
How do you study human speech while using ECoG?
play different sounds while using electrodes then measure brain activity, phonemes, filter data & look at high frequencies
many groups working on using ECoG, Utah arrays, or noninvasive EEG/fNIRs to decode thoughts in people who cannot speak
Types of Analysis
Peri-stimulus time histogram (PSTH) and Receptive field analysis
Peri-stimulus time histogram (PSTH)
make a plot that shows number of action potentials before/during/after stimulus, look at response timing + selectivity, line shows when it's on
Receptive field analysis
Play many different stimuli, see which cause the neuron to fire AP
can test hypotheses about processes that happen quickly
can know precisely where neural signals are coming from
Low temporal looks at things like
High temporal looks at things like
What can fNIRS test?
conversations, turn taking in people each with fNIRS cap
What can fMRI test?
listening to sentences, find where this processing happens in the brain
What can EEG test?
testing whether responses to phonemes differ for non-native vs native English listeners
language functions distributed across many brain areas
specific language functions localized to a particular region
Where is Broca's area?
foot of inferior frontal gyrus, above lateral fissure, anterior to percental gyrus
Lesions in Broca's area cause what?
apraxia of speech (disfluent production)
2nd frontal gyrus just above Broca's, across from hand/motor cortex
Lesions in Exner's center cause what?
agraphia (impairment in writing)
center/posterior parts of superior temporal gyrus, extends to supramarginal gyrus
Lesions in Wernicke's area cause what?
impair comprehensions of spoken language
adjacent to Wernicke's area
Lesions to supramarginal gyrus cause what?
impair syntax, semantics, and repetition
at the junction of temporal, parietal, and occipital lobes. at posterior part of the sulcus separating the superior temporal and middle temporal gyri
What is the angular gyrus important for?
reading, writing, and understanding sentences
The classic model
Broca's = language production ("non-fluent aphasia"), Wernicke's = language perception ("fluent aphasia"), Arcuate Fasiculus = connection between them
Critiques of classical model
Broca's is also involved in language comprehension, is wernicke's even real?
We know where Broca's is, but not what it does. We know what Wernicke's does but not where
Evidence for localizationist view
lesions can sometimes lead to specific deficits (ex: loss of knowledge about tools or animals)
Evidence for holist view
Differences in aphasias can be explained by a single "general language factor"
Localizationist or Holist?
the truth is probably somewhere in between
Criticisms of Neuropsychology
Lesion extent different in every patient, Lesions damage white & gray matter, Lesions symptoms are not stable, Many symptoms are not all or one but degree, Important functions may be redundantly represented
What does fMRI measure?
BOLD (blood oxygen level dependent signal), ratio of oxygenated to deoxygenated hemoglobin - more oxygen needed for brain activity! measured with magnetic fields
fMRI is ___ spatial and ___ temporal
What does PET measure?
metabolism of certain molecules
PET is __ spatial and __ temporal
What does EEG measure?
electrical potentials at the scalp, this reflects groups of neurons firing
EEG is __ spatial and __ temporal
What does fNIRS measure?
BOLD (blood oxygen level dependent signal), ratio of oxygenated to deoxygenated hemoglobin - more oxygen needed for brain activity! measured because they absorb light differently
fNIRS is __ spatial and __ temporal
What does Electrophysiology measure?
electrical signals = action potentials (voltage of the cell membrane either inside or outside cell)
Electrophysiology is __ spatial and __ temporal
What does ECoG measure?
electrical signals, but these are from many groups of neurons firing, similar to EEG
ECoG is __ spatial and __ temporal
What are sounds?
vibrations that travel through the air and propagate a pressure wave
Important parameters of sound waves
frequency & intensity/amplitude
# of waves in one second (Hz) - pitch
magnitude of movements (dB) - loudness
Speech sounds are the outcome of a combination of gestures of several organs including multiple __ and __ acoustic cues
Acoustic Cues in Speech
• "Bands" in the spectrogram: Pitch/harmonics, prosody/melody • Formants (vowel identity) • Voicing (voice onset time /ba/ vs /pa/) • Noise segments (sibilants and fricatives) • Silence (stops & plosives) • Duration and shape of formant transitions
Word comprehension relies on what?
lower spectral modulations (still need temporal content)
You get speaker identity from
spectral modulations (determines pitch)
What would the spectrogram of the sound that is heard from a limited number of electrodes in a cochlear implant look like?
smeared in frequency
orderly representation of frequencies from low to high
The Dual Stream Mode
Bilateral, very cortically focused (like classic model)
the computation of which sound frequencies are modulated at which rates
Example of spectrotemporal analysis
patients with electrodes listen to speech stimuli, record ECoG signals, determine which spectral or temporal modulations each area is most sensitive to
How can we see pitch?
using scalp electrodes (EEG) in the neural signal itself
FFR is different for native vs. non-native speakers
any change in frequency (how close the harmonics are - pitch)
any change in the spectrogram, independent of frequency
Vowels have more ___ modulation, stops have more ___ modulation
How do you interpret Visual Word Form Area graphs?
barplot shows activity for each stimulus
Properties of the visual word form area (VWFA)
• VWFA responds to printed words regardless of location • Detects identity of printed words (e.g. RAGE or rage) • Detects identity of words regardless of font • Has greater sensitivity to real than unreal printed words • Responds more to printed than spoken words (but may be activated during rhyme judgment!) • For congenitally blind people reading Braille, VWFA more active for real Braille than unreal Braille words!
For those who are illiterate VWFA may respond to ___ ___
Greater reading skills means ___ more VWFA activity for words
When we write, what do we activate first?
phonological and semantic structures of words
What is a grapheme?
smallest unit of a writing system - can be letter, character, digit, punctuation mark
What is allographic conversion?
translating abstract letter identities into concrete forms (upper, lower? cursive?)
What does disruptions to left ventral occipitotemproal cortex often cause?
impair both reading and writing
When patients receive treatment to help reading or writing, it can ...
improve the other modality
Reading and writing probably rely on what?
a single orthographic lexicon
How does the central part of the brain relate to writing?