Exam 1 Flashcards
When was modern Cognitive Neuroscience originated?
~1970s-1980s
Cognitive Neuroscience was born from the combination of what 3 related fields of research on the brain and behavior?
- Cognitive Psychology
- Neurology
- Neurophysiology/Neuroimaging
Explain the field of Cognitive Psychology
Studies how the brain works in healthy folks, data was explicitly behavior based (avoids brain)
Field of Neurology
How brain damage affects behavior in clinical patients, data was deficit based (behavior-brain linked)
Field Neurophysiology / Neuroimaging
How healthy brains work in animal model, later including humans with the development of noninvasive brain recording methods.
Folks from these 3 fields collaborated to investigate:
Brain Structure: distinct units, how they’re connected
Brain Function: how these units operate in real time
Consciousness: emergent property of brain function
Examples of “consciousness”
Awake vs. Asleep (or under anesthesia)
Attention vs. inattention, mind wandering
Imagining something far in the future, or long ago
Connecting concepts in novel ways, creativity
Self awareness: recognizing yourself as you, through time
Perspective-taking: seeing something from another’s eyes
Meta-awareness: knowing that you are thinking and more
What is consciousness?
Despite lots of investigation, there is little agreement about what consciousness is, and how it might be studied.
Over the last ~2 million years, the human cortex has nearly _______ in size.
Tripled in size
It’s tempting to link “consciousness” to cortex size
Cortex
Cortex = Cerebral Cortex (syn: Cerebrum, Forebrain)
Mostly Homogeneous tissue
Greatly expanded in primates, cetaceans
Critical to (but not sufficient for) “higher-order” cognition
Subcortex
Everything else in the brain:
-Cerebellum
-Thalamus
-Basal Ganglia
-Amygdala
-Hippocampus
-Midbrain
-Brainstem
Variable size and internal structure
Quite similar in structure & function with other mammals
Also essential to higher order cognition
Gyrus
Rounded protrusion of surface cortex -(“mountain”)
Sulcus
Depression in surface cortex (“valley”)
How much of the cortical surface is hidden in sulci and fissures (sulci within sulci)?
2/3
Purpose of Cortical “packaging”/”folding”
Cortical folding allows lots of tissue in a small space, and (maybe) speeds cortical processing time by keeping all brain regions relatively close together.
Where is the first stage of cortical processing
“Primary” Sensory Cortex
V1
Primary visual cortex
A1
Primary auditory cortex
S1
Sensory cortex
M1
Motor cortex
What brain structure is a possible consciousness “manager”
The Thalamus
Classical View of the Thalamus
The thalamus relays sensory and motor signals up to the cortical processing areas, and downstream to brainstem (except smell).
The thalamus was though of as a simple connection center, passing on signals from the body to the brain.
Modern View of the Thalamus
Recent work has identified that the structure of the thalamus is mostly (~80%) connections from one region of cortex to another region of cortex.
Instead of primarily carrying sensory input to cortex, and motor signals out to the body (“first order” connections), the thalamus is heavily involved in cortico-cortico connections (“higher order” connections).
What unique ability does the thalamus have?
The thalamus has the unique ability to switch from ‘burst’ to ‘tonic’ modes of signal transfer.
These firing modes appear to enhance or inhibit the ‘quality’ of a connection between brain regions.
How is the firing mode of the thalamus changed?
The firing mode is changed by relatively long (50-100ms) periods of excitatory or inhibitory input from brain stem & cortex.
“noisy” connection
Tonic mode (-65 mV)
“clean” connection
Burst mode (-75 mV)
How is the thalamus critical to “consciousness”
The thalamus seems to have the ability to connect and disconnect lots of brain region rapidly.
This thalamic structure and functional arrangement could provide a basic mechanism for orchestrating networks across the brain.
Nervous System hierarchy/ Organization
Nervous system is composed of two branches: the peripheral and central (brain and spinal cord)
The peripheral nervous system includes the autonomic and somatic nervous system
The autonomic nervous system includes the sympathetic and parasympathetic nervous system
Nervous System hierarchy/ Organization
Nervous system is composed of two branches: the peripheral and central (brain and spinal cord)
The peripheral nervous system includes the autonomic and somatic nervous system
The autonomic nervous system includes the sympathetic and parasympathetic nervous system
Autonomic Nervous System
Component of the Peripheral Nervous System
-controls self-regulated action of internal organs and glands
Somatic Nervous System
A component of the peripheral nervous system
Somatic nervous system controls voluntary movement of skeletal muscles
Sympathetic
Arousing
Parasympathetic
Calming
Main Role of Autonomic Nervous System
The autonomic nervous system is mostly concerned with housekeeping the body, but can show strong effects of mental state, anticipation
The autonomic nervous system is _________
Reciprocal; one branch holds primary control over a target organ at a given time.
The Sympathetic branch prepares the body for ______
intense action
Parasympathetic branch tends to ____
maintain body homeostasis and repair
except for digestion
Which branch of Autonomic Nervous system:
Constricts pupil
Parasympathetic branch
Which branch of Autonomic Nervous system:
Inhibits tear glands
Parasympathetic nervous system
Which branch of Autonomic Nervous system:
Increases salivation**
Parasympathetic nervous system
Which branch of Autonomic Nervous system:
Slows heart
Parasympathetic branch
Which branch of Autonomic Nervous system:
Constricts bronchi (breathe less rapidly)
Parasympathetic branch
Which branch of Autonomic Nervous system:
Increases digestive functions of stomach and pancreas
Parasympathetic
Which branch of Autonomic Nervous system:
Increases digestive functions of intestine
Parasympathetic
Which branch of Autonomic Nervous system:
Stimulates bladder contraction
Parasympathetic
Which branch of Autonomic Nervous system:
Stimulates blood flow to the genital organs (erection)
Parasympathetic
What percent of our body weight does our brain makeup?
Brains make up 2% of body weight
What % of metabolic resources does the brain consume?
20%
The vascular system of the brain is incredibly _____, and the blood-brain barrier is ______.
Dense; tight
In order to track brain activity, what is functional imaging dependent on?
Functional imaging is dependent on bloodflow to track brain activity.
Historical view of Glial cells vs Modern View
They were historically considered “support” cells for neurons.
Modern view suggests that glia serve many functions and contribute to brain function more than we know.
Approximately, what is the ratio of glial cells to neurons
1 glial cell for each neuron in the brain
**actual proportion is controversial (which gives insight to how little we actually know about glia)
What three glial cells are found in the central nervous system?
- Astrocytes (enable neurovascular coupling- critical to fMRI)
- Oligodendrocytes
- Microglial cell
What glial cell is found in the peripheral nervous system?
Schwann cell
Three main parts of a Neuron
- Dendrites (recieve input from other neurons)
- Soma (cell body) -contains the nucleus
- Axon (propogates action potential to synapse)
Inputs of Neurons
Input for Neurons includes excitatory or inhibitory signals from other neurons. These signals bind to dendrites and are received in the cell body.
Summation of a Neuron
at axon hillock (the site of transition between the cell body and the start of the axon)
-incoming signals (excitatory or inhibitory) from the dendrites accumulates to depolarize the cell to hit threshold to generate an action potential.
Output of Neurons
the output (action potential) travels down the axon to the synapse (releases neurotransmitters) with the next neuron
The synapse
no direct contact between neurons– just tiny space
Presynaptic neuron releases neurotransmitter (NT) into the synapse. which modulates activity of the postsynaptic neuron, depending on the NT and receptor type.
Electroencephalography (EEG)
real-time recording of the electrical activity of the cortex (non-cortical brain activity is missing from EEG)
In EEG’s Pyramidal neurons in the cortex are oriented in _______.
columns
-Pyramidal neurons are a common class of neuron found in the cerebral cortex of virtually every mammal.
As the pyramidal neurons in the cortex sum input from other neurons, what happens?
Their electrical charge becomes more voltage-negative near the outside surface of the cortex.
Real-time, continuous EEG
single sensor at top of head
What is EEG useful for tracking?
long-lasting ‘tonic’ mental states, like alertness or sleep
What could one see on an EEG recording for someone in deep sleep?
delta frequency band that is slow and has a speed of 1-4 Hz
What could one see on an EEG recording for someone in a drowsy state?
Theta frequency bands with a speed of 4-8 Hz
What could one see on an EEG recording for someone in a relaxed state
Alpha frequency bands that travel at a fast speed 12-30 Hz
Event-Related Potential (ERP)
Averaged segments of EEG over repeated trials. This flattens the background EEG and enhances the small but consistent ‘hidden signal’.
By taking the average of several trials, you create a clearer ERP.
What is the benefit of averaging EEGs
By averaging several trials of EEGs, this reveals the small, consistent ERP (event related potential) from the noisy EEG background.
This is similar to averaging the single pictures of a movie-the consistent elements remain.
In order for ERPs to be useful what needs to hold true?
the ERP must be consistent in timing and shape.
The averages of both groups need to line up to yield anything useful.
What drives early ERP components (~100ms after stimulus onset)
basic stimulus features like intensity
These are called exogenous components because they are determined outside the body.
What drives later ERP components (250+ ms after stimulus onset)
psychological meaning of stimuli
These are called endogenous components, because they are determined inside the body.
The first ERP component related to a psychological process was the P300 - a big increase in voltage after a rare event.
The P300 was (and is) a hot area of study because it revealed brain reactivity to ___________
Unexpected events, including missing events
The revealed brain reactivity to unexpected and missing events shows that P3 is not _________ but reflects ______
This shows that the P3 is not a sensory response— the P3 reflects a broken expectation.
Why are there problems in the ERP source localization?
The cerebral cortex of the brain is convoluted (densely folded).
Therefore, most parts of the cortex are not perpendicular to the scalp surface.
The negative voltage points in some other direction.
Depending on the _______ of active cortex, the scalp electrodes might ‘see’ a voltage positivity, negativity, or two areas of activity may cancel out, and no volatage will be seen.
Orientation
Where does the EEG not ‘see’ brain activity that we know exists (using f MRI)
in areas where the two hemispheres meet
Why is it when the farther the activity is from the scalp the weaker and more ‘cloudy’ the signal on ERP.
Volume conduction
as the signal travels, it spreads out, and loses strength
EEG/ERP Source Localization limitations
-folding/orientation of active cortex can cause voltage positivity, negativity, or two areas of activity may cancel out and no voltage will be seen
-Cerebral cortex is convolutes (densely folded) — most parts of cortex are not perpendicular to scalp surface
-doesn’t see brain activity where two hemisphere meets
-the deeper the activity is/farther from the scalp the weaker and more cloudy the signal is –this is bc of VOLUME CONDUCTION
-As signal travels, it spreads out, and loses strength
-thus strong EEG voltage could be from:
1) weak activity close to scalp
OR
2) Strong activity deeper in the brain
These several problems in localizing the origins of EEG?ERP leads to poor (~10cm) source location
MEG
Magnetoencephalography
A magnetic field wraps around all electrical currents. We can measure these tiny fields using an array of small detectors (SQUIDS)
SQUIDS
Superconducting quantum interference devices
Adavntage of MEG over EEG
MEG field is sharper bc they don’t spread out like electric fields (volume conduction) as they pass through the brain and skull
Only limitation of MEG
by the size and number of SQUIDS (small detectors that measure magnetic fields)
Why doesn’t everyone use MEG in cognitive neuroscience?
MEG loses sensitivity sharply about 5 cm from the SQUID
Thus MEG is blind to deep brain structures
Functional magnetic resonance imaging (fMRI)
“blobs on brains”
fMRI yields colorful images that represent the location of brain acitivity with good percision
3 elements of MRI
- Strong, fixed magnet (MAGNETIC)
- Radio emitter and reciever (RESONANCE)
- Weak, variable magnets (IMAGING)
Structural MRI
Detects density of water in tissue
Produces a stack of sharp images in ~15 mins
MRI yields high spatial resolution 3D snapshot of brain at one point in time
Functional MRI (fMRI)
involves repeated, lower res imaging of brain.
Interested in image intensity as it changes over time
Focuses on the small changes in signal intensity that accompany changes in local blood oxygenation (BOLD CONTRAST)
Blood Oxygen Level Dependent (BOLD) contrast: the source of fMRI signal
Brain activity requires oxygenated blood.
High activity states trigger local increases in blood flow and volume (via astrocytes)
Conveniently, the ‘resupply’ exceeds the demand by about 30%
This 30% excess of oxygenated blood increases fMRI signal intensity, bc oxygenated blood contains slightly less iron than deoxygenated blood. Iron ‘perturbs’ magnetic fields and causes the signal intensity to drop sharply
BOLD Signal timing
Late to show up, late to leave
brain/neural activity begins after 50 ms of scene presentation and drops off soon after the scene disappears
Bold signal onset is DELAYED, and lasts for several seconds after scene offset– bc it tracks the blood flow change, not the neural activity that triggered it.
MR Imaging weaknesses
BOLD signal is distorted or even absent near air cavities in head, causing
artifacts and “signal blowout”.
Because we need ~30 slices to sample the whole brain just once, the typical fMRI sampling rate (~ 2sec) is far slower than the speed of the brain. This is fMRI’s biggest weakness.
