Psy 362 exam 3
What are the functions of dreaming?
*they are poorly understood b/c they are difficult to study -dreaming seems to modulate associative memory networks (by promoting distant associations) -after dreaming, people often report finding more creative solutions -often dreams have bizarre content (distant associations) -dreams can modulate emotional states during waking (for example, in one study, the content of REM sleep predicted who became clinically depressed following divorce) -one idea is that dreaming provides the brain with a virtual reality model to "practice" during the night -*Note that the switching between NREM & REM sleep is regulated by complex interactions between mutually inhibiting "on" and "off" neurons
Electrodes are positioned over the scalp areas:
- F (Frontal), C (Central), T (Temporal), P (Parietal), O (Occipital) - Fz, Cz, Pz - "zero line" - midline electrodes - Odd numbers are on the left (F3, C3, T5, etc), even numbers are on the right (F4, C4, T6, etc)
An important aspect are the biophysical properties
- GEOMETRIC ALIGNMENT, CURRENT PROPAGATION: - pyramidal cells in the cortex are aligned into a palisade (they are parallel to each other) - their dendritic postsynaptic currents summate and can be picked up with EEG electrodes on the scalp
EEG is recorded as a continuous signal
- Spontaneous (resting) EEG: ALPHA OSCILLATIONS (8-12 Hz) are especially prominent. Alpha is the largest during "eyes closed" state of wakefulness -Alpha goes way ("alpha block") when the eyes are open
Dipolar current flow: propagates to the scalp where it is recorded as EEG
- The membrane at rest has a positive potential outside the cell - excitatory input (EPSP): Na+ influx into the cell: the positive ions enter the cell which leaves a deficit of positive charges and a relatively negative potential outside the cell
What causes the cell to fire - how is the resting membrane potential disturbed?
- an action potential of the presynaptic cell reaches the axon terminal (synaptic bouton) - Ca [2+] channels open up and Ca[2+] inions flow into the cell, allowing the synaptic vesicles to fuse with the cell membrane and release the neurotransmitter - the axon release neurotransmitter which diffuses in the cleft and binds to receptors on the postsynaptic membrane - the neurotransmitter causes channels on the postsynaptic membrane to open
neurotransmitter effects are terminated by
- degradation by enzymes - reuptake into the presynaptic cell - diffusion away from the synapse
LPC (Late Positive Complex)
- greater to repeated faces
Wakefulness is characterized by:
- high levels of sensorimotor activity (the neural gates are open for sensory input and motor output as new constantly communicate with the world around us) - sustainable neurotransmitter environment promoting arousal -some examples of neurotransmitters that are involved at higher levels: norepinephrine, histamine, serotonin, acetylcholine, etc) -*Note that histamine is also called a "wakefulness master" b/c it is highest during wakeful state. You may know it for its involvement in the inflammatory response and allergic reactions
Sleep occupies 1/3 of our lives. it is characterized by:
- higher threshold to sensory stimulation (which means that the sensory stimulation needs reach much higher levels to be registered - such as very loud sounds etc) - lower levels of motor output (while sleeping we are mostly immobile w/ minor changes in position) - dreaming
ERPs allow us to examine
- how the processing unfolds in time -at which latency a stimulus is first perceived as a face
inhibitory effects
- hyperpolarization -- the cell is less likely to fire - GABA
main advantage of iEEG:
- it can localize generators of the ERPs -the iEEG signal is larger and cleaner than when measured the scalp
EEG reflects postsynaptic potential directly WHAT IS EEG GOOD FOR AND HOW DO WE USE IT IN CLINICAL PRACTICE?
- it is used in clinical settings to monitor alertness, coma, anesthesia - it can indicate the level of cognitive engagement - it is used to create the biofeedback signal (to help people relax) - it is indispensable for studying seizures/epilepsy - it is useful for studying drug effects - it is needed to study sleep Downside: its spatial resolution is poor (it is difficult to figure out WHERE those currents were generated in the brain just by looking at EEG)
polysomnography
- multidimensional approach to study sleep that relies EEG and other physical measures such as EOG, EKG, EMG, breathing, blood oxygen levels, etc - it is used to diagnose sleep disorders - it also reveals sleep stages (sleep architecture): - 2 main types: NREM and REM
REM sleep
- occurs in greater proportion in later cycles - adults: 25%; elderly: 15%; premature infants: 70-80%; newborns: 50% - REM is present in humans, mammals, and birds; there is relatively more REM in predators - some marine mammals and birds sleep w/ one hemisphere at a time: whales don't seem to have REM sleep and seals also have no REM in water but on land they switch to REM sleep (REM sleep causes muscle paralysis which presents a problem in water)
Artifacts: important to use clean, artifact-free epochs for ERP averaging
-During preprocessing it is important to clean the data from artifacts that are usually much larger than the brain signal. Artifacts can be excised from data by removing noisy trials or by using correct algorithms
Electrodes are positioned on the scalp based on the INTERNATIONAL 10-20 MONTAGE SYSTEM as follows:
-measure the distance between the nation and the inion (in the sagittal view) -measure the distance between the two pre-auricular points (in coronal plane) -and then calculate 10% or 20% of those distances to determine electrode position
(1) the SINK
- positive Na+ ions flow into the cell resulting in negative external potential. *Note this is an ACTIVE process caused by synaptic events - as a result, there is a deficit of these positive ions (relative negativity) outside the cell which attracts other positive ions in the vicinity
(2) the source
- positive ions are passively attracted to the negative sink (there is no active, synaptic events causing the flow of ions) - area of positive voltage is the current source - the current flows toward the sink - this loop between the sink and source creates the current (the flow of charged ions) - the source can also be active: inhibitory postsynaptic potentials cause an influx of Cl- into the cell and an area of positive charges outside the membrane
REM characteristics
- rapid eye movements, faster pulse, and irregular breathing - functional paralysis (hyper polarization of motor neurons which cause inhibition); skeletal muscles are paralyzed to prevent the dreamer from acting out dreams - Dreaming: when awakened from REM sleep, subjects report dreaming over 80% of the time, but dreams can also occur at the onset of sleep. There is less dreaming during NREM cycles REM dreams are longer, more vivid, emotionally charged and bizarre - REM facilitates memory
excitatory effects
- resulting in depolarization and cell firing - glutamate, acetylcholine, dopamine, norepinephrine
intercrannial EEG (iEEG)
- surgery for individual who have seizures that are pharmocoresistant -iEEG is needed to localize epileptogenic zone
EEG is made possible by the alignment of pyramidal cells...
- synchronized input creates dipolar currents - volume conducted to the scalp -- measured as neg. or pos. potentials - conductivity barriers due to different tissue types
How does the membrane get depolarized? (what are post-synaptic potentials?)
- the cell will fire (generate an action potential) only when the postsynaptic potential reaches THRESHOLD (~ -40 to -55mV) at the axon hillock (trigger zone between the soma and the axon) - postsynaptic potentials are known as GRADED POTENTIALS - they reflect the summation of postsynaptic potentials, they are local and they weaken with distance
how does the membrane get depolarized? (what are postsynaptic potentials?)
- the chemically-gated ion channel (receptor) opens up to a certain type of ions that change the membrane potentials: EPSP & IPSP
Graded potentials - summation of postsynaptic potentials
- they DEPEND ON THE STRENGTH OF THE STIMULUS (e.g more neurotransmitter will cause stronger postsynaptic potentials) - The summation of postsynaptic potentials can be: - TEMPORAL (if they overlap in time) - Spatial (if they overlap in space)
N170
-(over the posterior temporal lobe, especially on the right side) is the earliest index of face recognition -"neural signature of face processing" -larger to faces than objects, cars, scrambled images -but smaller to upright faces compared to inverted and composite faces -N170 is usually not sensitive to repetition or familiarity - recognition happens later (termed N250)
B/c the current flows along the path of least resistance...
-B/c the current flows along the path of least resistance, there will be a wide distribution on the scalp (i.e the potential recorded by a particular electrode does NOT only reflect electrode under that electrode, but a summation of potentials generated at a distance) -Why is this important?- it means that it is difficult to localize the spatial pattern of activity (each electrode measures a summation of currents coming some distance, not just underneath)
EEG scalp recordings
-EEG is measured w/ small metal discs (electrodes) that can be attached to the scalp individually, but most commonly they are embedded in an electrode cap that is made from elastic fiber that mold's to each person's head. the cap also positions the electrodes in a comparable way on the scalp across people -the skin is slightly abraded/cleaned first -EEG washable paste or gel is applied to the electrodes to ensure good contact with the skin -EEG is typically recorded from 32 or 64 electrodes (but can be more)
ERP summary
-ERPs are derived from EEG by averaging time-locked EEG epochs across many trials -excellent temporal resolution -advantage: examine how brain processing unfolds in time (stages of processing) -disadvantage: poor spatial resolution (cannot localize generators)
Ground electrodes
-Ground electrodes eliminate the noise that is common to active and reference electrodes --- its placement is not crucial - differential amplifiers are used for EEG recordings b/c they subtract those noises that are common to bot active and reference electrodes and that come from the ground electrode. This results in clean signal - So the setup looks at the difference between: (active - ground) - (reference - ground) = Active - Reference - EEG IS THE DIFFERENCE BETWEEN THE ACTIVE AND REFERENCE ELECTRODES -important to have low electrode impedances (below 5 kOhms) which we get by ensuring good contact between electrodes and the skin
How does the membrane get depolarized? (what are postsynaptic potentials?)
-a single presynaptic potential is weak so the summation is needed to reach the threshold; if those postsynaptic potentials overlap in time and space, the are mostly excitatory, they will depolarize the membrane, build on each other and trigger inaction potential (e.g the neuron will fire) -postsyanaptic potentials (PSPs) are relatively SLOW (tens of mmillisecs) which makes it possible for them to overlap in time and summate
Epilepsy
-affects 3-4% and is th 4th common neurological problem after migraine, stroke, Alzheimer's -abnormal, hyper synchronous discharge of a population of neurons Epilepsy is suspected after two or more recurrent, unprovoked seizures
Noise
-background (spontaneous) brain activity. It is assumed that large artifacts such as eye blinks or movements etc. have already been cleaned/removed -noise is random with respect to the event -it is usually measured in the period before the stimulus onset in the averaged ERPs --> BASELINE -it cancels out when averaged across many trials -the baseline should be as flat as possible b/c the noise should average out to zero (there can be no signal before stimulus onset)
Simple partial
-consciousness is preserved which means that the person is alert, responsive, and can remember what happened during the seizure
EEG is recorded inside the brain w/ SEEG: Stereoencephalogy (depth electrodes)
-depth multi contact electrodes are implanted into the brain tissue at some depth -it relies on a 3D grid system that allows for stereotaxic navigation and electrode positioning through small holes in the skull
Based on such data across many patients, it is possible to formulate: Spatio-temporal Model of Cognitive Processing
-early processing in sensory-specific occipital areas (~100ms) -activity advances down the ventral visual system (ventral temporal) - material-specific encoding at ~170 ms in the fusiform gyrus (relatively more on the right to faces, on the left to words) -integration of semantic, memory, emotional associations in the cognitive context during ~230-700ms which results in conscious processing (based on interactive co-activation of the temporal and prefrontal areas)
EEG is very sensitive to other, non-neural sources of signal: Artifacts (large signal that does not originate from the brain)
-eye blinks are the major source of artifacts. They are much larger than the brain signal and are especially prominent over the frontal electrodes (close to the eyes) -lateral eye movements also cause artifacts - eye blinks and eye movements are measured as EOG b/c the cornea is electrically positive relative the retina -poor ground or poor electrode contact can result in noisy recordings
N400
-greater to novel faces -the longer-lasting negativity (N400) is elicited by meaningful stimuli -it reflects the COGNITIVE stage of processing which different types of input are integrated into a conscious recognition -*it is not evoked by simple, meaningless stimuli, such as clicks
Action potential
-if the cell is sufficiently depolarized (e.g if the summated EPSP reaches threshold - the negative potential is decreased sufficiently)), the cell fires it generates an AP - if the threshold is not reached, no AP - the AP moves down the axon very fast (1-2ms) - myelinated axons with regions without myelin (nodes of Ranvier)- the AP is regenerated at each node
neurotransmitters
-neurotransmitters are chemical substance that act to open or close chemically-gated ion channels. By changing membrane permeability they can have either excitatory or inhibitory effects
Generalized seizures
-seizures involve both hemispheres -common examples are: -Absence (6%) they are brief, start and end abruptly w/out warning -tonic-clonic seizures (23%) a.k.a "grand mal" or convulsive seizures: impaired consciousness w/ periods muscle stiffening and jerking of limbs -atonic: a sudden loss of posture resulting in falling -myoclonic: brief muscle jerks
Partial (focal) seizures
-seizures start in one part of the brain (57%)
semantic mismatch
-sentences that had congruent or incongruent endings - incongruent ending had a greater negativity N400 peaking ~400ms after onset -N400 is sensitive to meaning and congruence w/ context and is NOT perceived by the brain as an oddball in a sense of the meaningless stimuli (tones) that are presented infrequently in an otherwise predictable sequence
What are sleep functions:
-sleep is restorative. It is also necessary for survival. Sleep deprivation results in disruption of metabolism and death (in rats, it is fatal after 4-6weeks) -conservation of energy -anabolism ("building up of proteins, muscles, etc) -hormone regulation (growth hormone is released especially during sleep) - memory consolidation: sleep is necessary for retention
Experimental setup
-stimuli (e.g faces) are presented on the screen (or via headphones) by a presentation computer -stimulus markers are sent out at the same time to the EEG recording computer -EEG signal is recorded continuously but these markers make it possible to segment EEG data into epochs (e.g i sec from onset) EEG epochs are then averaged together to obtain ERPs *ERPs can be averaged w/ respect to different types of events such as: 1) stimulus-onset - to see what happens in the brain during stimulus processing 2)response (e.g button pressing) - to see what happens in the brain during response preparation 3) any discreet event (can be evoked by thought)
EEG is recorded inside the brain w/: ECoG: electrocorticography
-subdural electrode strips or grids (placed on the exposure surface of the brain, below the dura mater) -preferred for situations in which the epileptogenic zone involves lateral cerebral convexity -microECoG multi arrays can also be implanted alongside electrode grids to provide insight into micro physiology of the cortex (especially in the epileptogenic zone)
How do these currents propagate to the scalp?
-the current is generated by many small neighboring dipoles (sink - source configurations on each neuron which, at a distance, can be modeled as a dipole) -the current flows in all directions in the volume of the head -but different tissue types differ in their conductivity as some are more conductive than others example: CSF is more conductive than the brain tissue, which is more conductive than the skull (bone is a very poor conductor), etc
N250
-the earliest index of memory engagement is visible at N250, followed by N400 (semantic processing) -at this point, the anterior temporal lobe (and the hippocampus) is activated, followed by engagement of the frontal and temporal cortices that are needed for cognitive integration
ERP averaging assumptions
-the signal (brain response to a particular event) remains the same on each trial -the noise is random so it will decrease as the number of trials increases - signal-to-noise (SNR) expresses the relative strength of the signal (ERP after stimulus onset) compared to noise (ERP before the stimulus) -averaging increases SNR by decreasing the influence of random activity -ERPs need to be perfectly time-locked to stimulus onset
When compared to auditory oddball tasks
-tones evoke a greater N100 and rare tones evoke a greater P300 -faces evoke a N170, N40 (larger to novel faces), a late positivity complex (greater to repeated faces) -*Note that the N400 is evoked by stimuli that carry meaning and it reflects the stage of cognitive processing
ERPs are classified based on their
1) sensory modality (visual, auditory, somato-sensory) 2) latency - early- peaking before 100ms; primarily depend on the sensory features --> low level sensory processing -late - peaking after 150ms; increased influence of cognitive processes (attention, meaning, etc)
complex partial
36% of seizures -consciousness is impaired (the person cannot communicate and does not remember what happened during the seizure) -AURAS sometimes serve as a warning that a seizure is about to happen
T OR F: EEG is a result of a summated current flow through the brain, skull, scalp tissue, etc
True
the current sink is characterized by the following: A. POSITIVELY CHARGED Na+ FLOWS INTO THE CELL B.positively charged K+ ions flow into the cell C. there is no ion movement b/c of the resting membrane potential D. ALL OF THE ABOVE
A. POSITIVELY CHARGED Na+ IONS FLOW INTO THE CELL
IMPORTANT: EEG is generated by postsynaptic currents and NOT by action potentials -- why?
Action potentials are too fast (~1ms) and not spatially aligned --> cannot be synchronized/summated in time or space
T OR F: if the sum of an EPSP causes a postsynaptic potential to reach the threshold, then the postsynaptic potential will generate an AP
True
At the resting, a higher concentration gradient of ____ is found outside a neuron and a higher concentration of ____ is found inside a neuron A. K+; Na+ B. Na+; K+ C. dopamine; serotonin D. serotonin; dopamine
B. Na+; K+
The ease with which a cell membrane will permit ions to cross it is referred to as A. the concentration gradient B. permeability C. the action potential D. conductivity
B. permeability
The value of the membrane potential to which an axon must be depolarized to initiate an action potential is called the ____ potential for that neuron A.graded B.resting C.threshold D.refractory
C. threshold
inhibitory postsynaptic potentials (IPSP) are characterized by the following A. the cell becomes hyper polarized B.chloride enters the cell C. the cell is likely to fire D. ALL OF THE ABOVE
D. ALL OF THE ABOVE - the cell becomes hyperpolarized - chloride enters the cell - the cell is less likely to fire
Dipolar current flow is characterized by: A.pyramidal cells are aligned in parallel B. the is synchronized input into many cells C. postsynaptic potentials summate across large neuronal envelopes D. ALL OF THE ABOVE
D. ALL OF THE ABOVE
the cell is more likely to fire if the following happens near the trigger zone: A. there is sufficient summation of membrane depolarization B. membrane potential reaches the threshold C. there is sufficient excretory potential D.ALL OF THE ABOVE
D. ALL OF THE ABOVE - there is sufficient summation of membrane depolarization - membrane potential reaches the threshold - there is sufficient excretory potential
GABA is an ____ neurotransmitter which cause ___ of the cell membrane
GABA is an inhibitory neurotransmitter which cause hyper polarized of the cell membrane
which neurotransmitter is called the "wakefulness master"
Histamine
Synaptic release of an excitatory neurotransmitter (glutamates) results in A. opening of postsynaptic Na+ channels B. depolarization of the postsynaptic membrane C. excitatory postsynaptic potentials D.all of the above
D. all of the above
one of the characteristics of graded potentials is that they: A. are the same as resting potentials B. decay with time C. decay in space D. b and c
D. b and c (decay with time; decay in space)
resting potential is an electrochemical balance achieved by: A. hyper polarization B. diffusion force C.electrical force D. b and c
D. b and c (diffusion and electrical force)
Basic recording setup
EEG MEASURES THE POTENTIAL DIFFERENCE BETWEEN THE ACTIVE AND THE REFERENCE ELECTRODES - it is measured as voltage (in mV on the scalp) - active electrode (should be positioned near the active area of interest) -reference electrode (should be positioned far from the active area of interest - e.g mastoid bones, the nose) --- Why? B/c EEG measure the difference in potentials between the active and the reference electrodes. If they were next to each other, the common activity would be subtracted out
T OR F: hyper polarization makes the inside of the cell more positive and more likely to generate an AP
False
T OR F: the resting potential of a neuron is typically +40 to +90mV
False
EPSP (inhibitory postsynaptic potential)
IPSP is generate when an inhibitory neurotransmitter(GABA) is released into the synapse - GABA opens chloride channels which results in the Cl- influx - the membrane potential becomes MORE NEGATIVE than the resting potential --> the cell is HYPERPOLARIZED and less likely to fire - sodium-potassium pumps help restore the neuron back to its resting potential
EEG defined sleep stages: There are several sleep stages including...
N1 (NREM stage 1): transition from alpha (8-12 hz) to theta (4-7hz) - this is a period of somnolence (drowsy) sleep, some twitches and jerks caused by muscle contractions, hallucination N2: a true sleep state, 40-50% of sleep time - motor activity decreases - characterized by spindles and K-complexes N3: deep sleep (slow wave sleep) - delta wave (0.5 - 2hz). 20% of sleep time. Greater proportion of deep sleep (N3) earlier in the night, earlier sleep cycles. Memories encoded by the hippocampus are distributed into the neocortex for a long-term consolidation -The FIRST REM SLEEP occurs 70-90min after we fall asleep. The proportion of REM sleep increases with later sleep cycles and before we wake up. If we don't have REM sleep one night, we will go to REM sleep faster the next night and stay in it longer to make up for the deficit
Depth EEG indicates
N170 is generated in the fusiform gyrus (note that local generation is indicated by steep voltage changes and inversions) the N170 in the fusiform gyrus is much larger to faces than to words -late deflections (after 300-400ms) are seen to both words and faces and are comparable in the anterior temporal and inferior prefrontal cortex --> cognitive processing and integration stage
Sleep has a ____ to sensory stimulation
Sleep has a HIGHER THRESHOLD to sensory stimulation
a cell is likely to fire if the following happens near the axon hillock (the trigger zone)
The membrane is sufficiently depolarized (less negative)
The potentials recorded at the scalp are positive or negative, depending on the dipole orientation
The potentials recorded at the scalp are positive or negative, depending on the dipole orientation. The polarity will be determined by the pole closest to the electrode (i.e if the sink is closest to the electrode, it will be reflected in the negativity on the scalp) *Note that THE SCALP POSITIVITY OR NEGATIVITY IS NOT RELATED TO INHIBITION OR EXCITATION
When released into the synaptic cleft, GABA causes chloride channels to open up which results in ____, making the inside of the cell more ____
When released into the synaptic cleft, GABA causes chloride channels to open which results in chloride influx into the cell, making the inside of the cell more negative (less likely to fire)
a current sink his generated outside the membrane when:
a current sink is generated outside the membrane when positively charge Na+ ions flow into the cell, which is going to make the outside relatively negative)
oddball task
a series of frequent, repeating stimuli interspersed w/ occasional rare stimuli (~20-25%) which are perceived as oddballs (surprises) -the oddball stimuli a larger positivity (P3 or P300) -*Note frequents do not evoke the P300 b/ they are anticipated -P300 is sensitive too stimulus probability, attention. It is decreased across various brain-based disorders
EPSP (excitatory postsynaptic potential)
an excitatory neuron (glutamate) opens Na+ channels resulting in Na+ influx into the cell which DEPOLARIZES the cell (decreases its negative resting potential making the inside a bit more positive) --> the cell is DEPOLARIZED and is more likely to fire (e.g when it reaches -55mV) -sodium-potassium pumps help restore the neuron back to its resting potential
dipole
formed by two poles with opposing charges
P100
generated in the visual cortex, it does not differentiate between faces and non faces (pixelated images) b/c it simply reflects the very low-level sensory visual processing
NREM sleep
includes stages 1 to 3/4 and these stages are longer earlier in the night
sleep and alcohol
it helps people fall asleep b/c increases inhibition (it increases GABA and decreases glutamate), but it disturbs sleep cycles - it decreases REM, resulting in lighter cycles, it increases apnea (breathing problems)
sink
negative charges (where Na+ flows INTO the cell)
If neuron A causes neuron B to become hyperpolarized relative to B's resting state...
neuron B is less likely to release neurotransmitter molecules from its own axon terminal
The term concentration gradient refers to a difference in the
number of ions on the opposite sides of the cell membrane
source
positive charges (positive ions flow towards the negative sink) *Note that in the electrical field positive charges always flow towards the negative charges
neuronal signaling
synaptic events at the membrane that change the membrane potential (causes a change in voltage)
current
the flow electrical charge - due to the movement of charged ions
potential
the ions (charges) are separated so there is a potential for the ions (charges) to move along the gradient
voltage
the measure of potential energy generated by separated charges -always measured between two points (e.g inside vs outside of cell)
Synapse
the point of communication between two cells: the presynaptic cell releases a neurotransmitter into the synaptic cleft (a very tiny space between the cells as the don't actually touch). *Note that each neuron has tens of thousands synapses. Most of them are located on the dendritic spines (but NOT on the axon which transmits the electrical impulse to the next cell)
The sink and source are two poles of a dipole
the sink and the source are two poles of a dipole (their positive/negative imbalance causes ionic charges to move w/in the extra- and intracellular liquid), w/ special relevance of the extracellular currents that propagate through the head volume, they are conducted by the brain tissue, especially by the cerebrospinal fluid, less so by the bone but they reach the scalp where are recorded as EEG
You are most likely to be in the stage N3/4 of the sleep cycle...
you are most likely to be in the stage N3/4 of the sleep cycle when the slow delta waves are prominent
