EEG, EVOKED POTENTIALS, MEMORY

EEG, EVOKED POTENTIALS,MEMORYOlga Vajnerová,Department of Physiology,2nd Medical School, Charles University Prague, 2019

82. EEG, evoked potentials87. Types of memory88. Principle of engram formation

EEG

EEG - electroencephalographyRegistration of electrical brain potentials measured formtha surface of the scullIt reflects function properties of the brainRichard Caton 1875 – 1. Registration of ECoG andevoked potentialsHans Berger (Swiss psychiatrist) 1929 – human EEG, basicrhythm of electrical activity alfa (8-13Hz) and beta (14-30)After 1945 – EEG as a clinical inspection

ecord(registration, paper)

EEG activity is mostly rhytmic and of sinusoidal shapeFrequency and amplitude is judgedRhythm 14-30 HzRhythm 8-13 Hz(quiet wakefulness)Rhythm 4-7 HzRhythm 3 and less Hz

Normal EEG – lokalization of graphoelement typesFrontal - activityFistUnbend fingersparietal – , rolandicrhythmTemporal , activityEyes openEyes closedTemporo-parietooccipital - activityPodle Faber Elektroencefalografie

alfa –Eyes closedbeta –Eyes openbetathetadelta – somnolence, sleep

Kandel E.R. et al: Principles of neural science. New York 2000

At what age the „adult“ EEG can be recorded?From the birthOne year6 years12 years18 years

Ontogenesis EEGUntil 1 year – (1-3 Hz) not too regular, high amplitude,Is not blocked by eye opening1- 3 years - rhythm (4-7 Hz)3-5 let – more regular prealfa (6-8 Hz)Attenuation by opening eye isimperfectIs blocked by eye opening5-7 let – regular (8-13Hz) medial voltage,frontally Very good reactivity

Where is the origin of electricactivity measured as EEG?EEG is moustlyEPSP Excitatory postsynapticpotencialsPyramidalneuronIPSP Inhibitory postsynapticpotencialsKandel E.R. et al: Principles of neural science. New York 2000

Kandel E.R. et al: Principles of neural science. New York 2000

EEG activity is mostly rhytmicWhere in the brain this sychronous activity isgenerated?

Thalamocortical system(thalamic activity isrhytmic)

Reticular ascending system RASFrederic Bremer (30. of 20 century)Cerveau isolé(between colliculi superiores and inferiores)Unconsciousness, EEG sleep typeEncephal isolé (over C1)Sleep and wakefulness are changing

Wakefulness – vigilityReticular ascending system RASThalamocortical sychronization isdisturbed(thalamic activity is not rhytmical)

Evoked Potentials

Average evoked potentialsEEG changes bind to sensory, motor or cognitive eventsEvent-related EEG potentialsRoutine procedure of clinical EEG laboratories from 1980sValuable tool for testing afferent functionsSensory evoked potentialsVisual (VEP)Auditory (BAEP)Somatosensory (SSEP)

Visual-evoked potentials (VEP)Electrical activity induced in visual cortex by light stimuliAnatomical basis of the VEP:RetinaRods and ConesBipolar neuronsGanglion cellsOptic nerveOptic chiasmOptic tractLateral geniculate bodyOptic radiationOccipital lobe, visual cortex

Visual evoked potentials (VEP)

Electrical activity – electrodes placed on the patient’s scalpEvoked electrical activity appears against a background ofspontaneous electrical activity.Evoked activity a signalBackground activity a noiseSignal lower amplitude than noise, it may go undetected (hidden ormasked by the noise)Solution- by increasing amplitude of the signal – intensity of stimulation-by reducing the amount of the noise

How to reduce the amount of the noise-Superimposition

How to reduce theamount of the noiseSimplified diagramillustrating howcoherent averagingenhances a low levelsignal (coherent EPtime locked to theevoking stimulus)

Description of waveforms:NORMAL VEP OF RIGHT EYEpeaks (positive deflection)troughs (negative deflection)Measures:1. Latency of peaks and troughs fromthe time of stimulation2. Time elapsing between peaksand/or troughs3. Amplitude of peaks and troughsComparison of the patient’s recordedwaveforms with normative data

VEPs as a tool in the diagnosisMultiple sclerosis:Excessive interocular difference in P100 latencyProlonged absolute latencyDecreased amplitudeCompression of optic nerve (optic nerve glioma), optic chiasm(tumor of pituitary gland)

Epileptic seizures are characterized by followingdisturbances:occur in attacks, abrupt onsetusually accompanied by disturbances of consciousnessusually accompanied by disturbances of motor and/or sensoryfunctions and/or vegetative symptomsabnormal EEG recordings enable to reveal the focus ofepileptic activity

SeizuresI. Partial (focal)a simple partial seizures (without alternation ofconsciousness)b complex partial seizures (with impairment ofconsciousnessc comples partial seizures evolving tosecondarily generalized seizuresII. Generalized seizures (simultaneous disruption of normalbrain activity in both hemispheres)(convulsive or noncolvulsive)a absence (petit mal)b tonic-clonic (grand mal)

Typical epileptic grafoelements in EEGEyes openAlpha activitySpike and wave activityPetit mal (absence)Grand malTonic phaseTemporal seizure partial seizurewith complex symptomatologyclonicTheta až delta aktivitaSepto-hipocampal systemBeta aktivita 15-20 Hzunconsciousness(coma)

VideoEpileptic seizure – petit mal.

VideoEpileptic seizure - grand malThis 40 year-old patient had epilepsy worsened by aninappriopriate change in his antiepileptic treatment.Seizure begins by a sudden scream with bilateral axial flexionwith an internal rotation of both upper limbs.A slight non-forced rotation of head to the right is thenfollowed by a clonic phase.A second tonic phase occurs 55 seconds after seizue onset,followed by bilateral clonic jerks, a stertorous breathe.Post-ictal headache and limb stiffness.

Memory

Memoryabilityto accept information (encoding)to store (storage)to retrieve (retrieval)information from NS

Memory involves at least four distinct processes:Encoding - incoming information must beperceivedConsolidation – newly stored information is labile, tomake it more stable (expression of genes, structuralchanges).Evidence: Retrograde amnesia - a person who hasbeen knocked unconscious selectively loses memoryfor events that occured before the blow.Storage- to retain over time, almost unlimited capacityRetrieval – to bring different kinds of information together,it is constructive process, it is subject to distortion

Memory and learning is the same(Psychology: Learning gradual construction ofthe long term memory pathway)Engram (memory trace) Memory is not homogeneous Duration, persistence Brain structures Molecular mechanisms

Memory88. Principle of engram formation

Donald Olding Hebb*1904 †1985Canadian psychologistHebb's Law."Neurons that fire together wire together."Hebbian theory:When an axon of cell A is near enough to excite cell B and repeatedly orpersistently takes part in firing it, some growth process or metabolic changetakes place in one or both cells such that A's efficiency, as one of the cells firingB, is increased

Cell and molecular mechanisms ofmemory engramPosttetanic potentiation (short termpotentiation)Long term potentiation LTP

Posttetanic potentiationLarge Ca2 influx. Saturationof the various Ca2 bufferingsystems (ER, mitochondia)Temporary excess of Ca2 iscalled residual Ca2 .Concentration of free Ca2 increases the amount oftransmitter released

Posttetanic potentiationA hight rate ofstimulation of thepresynaptic neuronA gradual increase inthe amplitude of thepostsynaptic potentialPostsynaptic potential increases in size potentiationThe enhancement in the strength of the synapse represents storageof information about previous activityIt can lasts minutes but can persist for an hour.An elementary form of memory

Long term potentiation LTPNMDA - N-methyl-D-aspartatereceptorAMPA - α-amino-3-hydroxy-5-methyl-4isoxazolepropionic acid receptor

NMDA – glutamatereceptor

Long term potentiation LTPGlutamate synapseIonotropic receptors(directly gated):Both NMDA receptorsand non NMDA (AMPA)receptors

Long term potentiation1. Increases the sensitivity2. Increases the number ofpostsynaptic AMPAreceptors3. enhancement oftransmitter release inpraesynaptic neuron4. New synapses

Memory87. Types of memory

Sensory memory is the shortest-term element of memory. It is the ability to retainimpressions of sensory information after the original stimuli have ended.Short-term memory – lasts for seconds up to a minutesLong-term memory – weeks, months, years, for the rest of the life of an organism(permanent memory)Sensory memoryvisual (iconic)auditory (echoic)exploring objects through touch(haptic)

A scheme of memory processes that includes encoding,consolidation and retrieval

Iconic (visual) – reflects the activity of sensory buffers, continuation of sensoryneural activityIconic memory (visual persistence, example burning ring)George Sperling 1960Experiment:whole-report procedurePresentation 50 msRecall of 3-5 symbolsIn Sternberg R.J.: Kognitivní psychologie, Portál,Praha 2002: s. 187.

Iconic (visual)George Sperling 1960 – Iconic memory testExperiment:partial-report procedurePresentation 50 msCued recall – The frequency of the tone(high, medium, or low) indicated whichset of characters within the display wereto be reportedRecall of 9 symbolsSperling's original partial report paradigmIconic memory is described as a very brief ( 1000 ms), pre-categorical,high capacity memory store (approximatelly 9 to 12 items)

Short-term memoryseconds up to a minutesThe capacity of 7 2 items

Short term verbal memoryEbbinghaus curveprimacynoveltyImportance of succession in seriesPrimacy effect and the effect of novelty

Verbal memoryWho remembered the word assBetter we remember:personally interestingunusualinvokes emotionswhat has an erotic subtextwhat makes good shape

Long term memory1850 - 1909

Long term memory

Effective learningfirst repetitionin 2 hourssecond repetition the same day in the eveningthird repetitionafter 2 days

Short-term memory has the capacityof 7 2 usmofrotan But the items must be known for us

Long term memoryPacient H.M.Anterograde amnesiaScoville, Milnerová, 1957In Kandel 2000

H.M. was taught to trace between two outlines of a starwhile viewing his hand in a mirror

Long term memory classificationDeclarativeExplicitEpisodicStore itNonassociativeAssociativelearning

Regions of the human brain thathave been implicated in theformulation of long-term declarativememories.HippocampusFornixDorsal thalamusAmygdalaCorpora mammilaria

Long term memory classificationDeclarativeExplicitEpisodicStore itNonassociativeEndel Tulving 1972, on bases of Wildera Penfield experimentsAssociativelearning

Long term memory classificationDeclarativeExplicitEpisodicStore eventsautobiographicalSemanticStore factsNondeclarativeImplicitNonassociativeEndel Tulving 1972, on bases of Wildera Penfield experimentsAssociativelearning

Blue velvet arenaSpatial memory (a type ofdeclarative memory)

Long term memory classificationDeclarativeExplicitEpizodicStore eventsautobiograficSemanticStore iveImplicitNonassociativeNo relationbetween twoor morestimuli,behavior anditsconsequence.Associativelearning

Long term ing clock

Long term memoryNondeclarativeNon-associativeHabituationAn animal responds less andless strongly to uniformgentle taps on its surface.Sensitization

Long term memoryNondeclarativenonassociateveSensitizationBy a strong stimulation.A single electrical shock tothe skin.Stronger reaction to theweak tap.

Long term memoryNondeclarativenonassociateveImprinting

Konrad LorenzGreylag geeseincubator-hatched geese wouldimprint on the first suitable movingstimulusthe goslings would imprint on Lorenzhimself

Konrad LorenzCritical periodimprinted goslings

DeclarativeExplicitNondeclarativeImplicitLong term memoryEpizodicStore eventsautobiograficSemanticStore factsassociativeNonlearning – relationassociativebetweenstimulus-responsetwo or morestimuli, events,behavior – itsconsequenceclassical conditioninginstrumental, operantconditioning (standard or motorlearning)conditioned taste aversionpriming