Neuro - EEGs And EPs Flashcards
Define: Latency
Time between stimulus and response (speed = myelinated not)
Define: Amplitude
An expression of the number of recruited neurones and their synchrony (exact timing)
What is the difference between evoked and emitted potentials?
Evoked: responses modulated by the physical properties of the stimulus
Emitted/event related = responses dependent on higher order evaluation of the stimulus
What drives the ionic electrical currents that are measured during an EEG and EP? A. Presynaptic potentials B. Postsynaptic potentials C. Synaptic plasticity D. Tiny cars
B
What are the properties of the response which allow the extraction of the signal from the noise?
Evoked responses have the same spacial orientation/fixed polarity and the same latency
This allows for the summation of synchronous activity and the averaging out of events which are not happening at the same time and phase
Why can you not place the reference electrode far away e.g. The foot?
Needs to be placed close enough so it contains as much of the noise as would be in the area of interest but not the signal.
This is because the differential amplifier in the system then takes these 2 inputs (from the site of interest =Signal+noise, reference=noise) and takes one from the other to selectively as possible just get the signal of interest
What is sampling rate frequency?
An analogue signal from the patient is converted into a digital signal by the EP machine in order to be processed (filtering…) and visualised on screen.
The analogue to digital converter takes what’s happening at frequent regular intervals = sample points
Aim is to maintain clarity of wave when reconstructed onscreen without producing masses and masses of data.
What is cortical tonotopy?
The primary auditory cortex is arranged according to what frequency input it receives:
Anterior - low pitches
Posterior - high pitches
AEPs - match wave/inter peak latency to location in the pathway:
Wave I, Wave II,
Wave III, Wave IV, Wave V, I-V IPL, I-III IPL
Superior Olivary complex Inferior colliculus Proximal VIII nerve-cochlea nucleus Useful for retro-cochlear pathology Inferior colliculus Central Conduction time VIII Nerve
Wave I: VIII nerve
Wave II: proximal VIII nerve- cochlea nucleus
Wave III: Superior Olivary complex
Wave IV: Lateral Lemniscus
Wave V: Inferior colliculus
I-V IPL: Central conduction time
I-III IPL: useful for retro cochlear pathology
