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46 Cards in this Set
- Front
- Back
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What is a technique for studying the ensemble properties of the cortex that recrod activity of many cortical areas simultaneously? |
Electroencephalogram (EEG) |
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What is an electrocorticogram? |
ECoG Macroelectrodes that record summated acitivty when the cortical surface is exposed during surgery |
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What is an EEG? |
A measure of the extracellular current flow associated with the summed activity of many individual neurons Measures postsynaptic potentials rather than action potentials |
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What electrodes are needed for EEG? |
Active electrode: placed over site of neuronal activity Indifferent electrode: placed at some distance from the active electrode |
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In what domains are EEGs analyzed? |
Temporal (frequency) and spatial |
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What are the dominant frequency bands in EEGs? |
Alpha, beta, delta, and theta |
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Describe alpha waves. |
Relaxed wakefulness Parietal and occipital |
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Describe beta waves. |
Frontal regions Intense mental activity Smallest amplitude |
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Describe delta and theta waves. |
Associated with sleep Largest amplitudes |
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What is optical imaging? |
High-resolution spatial record of activity in population using voltage-sensitive dyes Some neurons emit signals based on their intrinsic fluorescence Invasive |
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What is the principal source of EEG potentials? |
Pyramidal cells |
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How do sensory-evoked potentials differ from event-related potentials? |
Event-related are dependent on the context in which the stimulus is presented (expected or a surprise) (typically longer latencies) |
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What are sensory-evoked potentials useful for? |
Assessing function of sensory systems or evaluating demyelinating disease |
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What is volume conduction? |
Describes the flow of ionic current generated by nerve cells through the extracellular space EEG and EKG |
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What is Rm vs Rex? |
Rm is the membrane resistence Rex is the extracellular resistance |
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Describe the extracellular resistance. |
Extremely small compared to membrane Yields small change in voltage when current flows (explains why EEG potentials are so small) |
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What is the site of inward current called? |
Sink |
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What is the extracellular potential at the sink? |
Negative |
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What is the opposing force of the sink? |
Source |
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How does signal decrease with distance? |
Square root of the distance (also contributes to small potential measured in EEG) |
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What is the initial cortical response to thalamic input? |
Formation of a sink in deeper layers and a source superficially |
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What could cause a positive wave recording? |
Either superficial excitation or deep inhibition |
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What does the EEG primarily reflect? |
Synaptic potentials in pyramidal cells, APs contribute little Extracellular current flow |
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Why do pyramidal cells contribute more than nonpyramidal cells to the EEG? |
Pyramidal cells are parallel to one another |
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Why do synaptic potentials contribute more than action potentials to the EEG? |
Synaptic potentials are slower than APs so they can summate |
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What is epilepsy? |
Synchronous discharge that produces stereotyped and involuntary paroxysmal alterations in behavior Jerking movements, transient loss of awareness, and even massive convulsions, and loss of consciousness |
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What can cause a seizure? |
Trauma, oxygen deprivation, infection, and toxic states In half, no specific causative factors |
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What are the two types of epileptic seizres? |
Partial and generalized |
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Describe partial seizures. |
Focal seizures Begins in a restricted brain region and either remains localized or spreads to adjacent cortex Don't necessarily disrupt consciousness |
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What must happen for consciousness to be lost? |
Epileptic activity must spread to the other hemispheres |
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What are psychomotor seizures? |
Complex partial seizures Involve limbic system |
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What is the EEG signature of a focal signature? |
EEG spike Brief, pointed wave |
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Describe generalized epilepsy |
Nonfocal epilepsy Large parts of the brain from the outset Invariably loss of consciousness EEG spikes all over the skull simultaneously |
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What are the different forms of generalized seizures? |
Petit mal and grand mal (more prominent) |
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Describe petit mal seizures. |
Begin during childhood Transient loss of consciousness (absence seizure) Characteristic discharge Interrupt perception, cognition, and membry Function returns immediately Muscle tone is maintained |
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Describe grand mal seizures. |
Abrupt loss of consciousness and postural control Falls to ground an dhas tonic-clonic movements (increased muscle tone (tonic) alternating with jerkign movements (clonic) Loss of consciousness and behavioral changes may persist |
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How would you induce a focal seizure? |
Apply convulsant drugs transiently to the surface of the cortex (acute focal epilepsy; no cell morphological changes) Direct application of penicillin blocks GABA Topical application of alumina cream (chronic focal epilepsy; morphological changes) Kindling (repeated electrical stimulation) |
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How would you induce a generalized seizure? |
Penicillin at toxic doses administered systemically |
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What underlies focal seizures? |
A depolarization shift |
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What is the first abnormal electrical event of a focal seizure? |
Interictal spikes: intermittent high-voltage negative waves Then low-voltage fast waves riding on a crest |
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What is thought to cause the paroxysmal depolarization shift? |
Generated by an EPSP that is enhanced and amplified by intrinsic (voltage-dependent) membrane responses Could be due to reduction of inhibition |
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What connections are responsible for synchronizing discharge in an epileptic focus? |
Excitatory connections between cortical neurons |
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How might seizure spread be limited? |
Synapse inhibition; depolarization shift is followed by a period of hyperpolarization |
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What is the process of brain slice preparation? |
Quickly remove and immerse in chilled saline Section tissue with microtome, reserving basic circuitry Place in recording chamber |
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What are two advantages of recording from brain slices? |
1) More stable recordings because there are no mechanical pulsations due to respiration or pumping of blood (can record from fine processes, such as dendrites) 2) Tissue is visualized under a microscope so individual neurons can be identified, facilitating patch clamping |
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What is the signature of generalized seizure in EEG? |
Spike-wave discharge present simultaneously over the entire brain |
