Lecture III Flashcards
Single-unit recording (SUR)
Recording electrophysiological activity (APs) from a single neuron.
Very high spatial resolution.
High temporal resolution.
Differences of SUR with EEG (2):
SUR more localized - better spatial resolution.
SUR measures APs - EEG measures EPSPs/IPSPs.
To study SUR (4 steps):
Record raw electrical fields inside the brain.
Then filter the signal.
Then start identifying different units/neurons.
Analyze events.
Low-pass filter
Filters out LFPs coming from surrounding neurons to use - only LFPs from surrounding.
High-pass filter
Filters out APs coming from target neurons to use.
Low-pass filter and frequencies
Low-pass filter - only low frequencies can pass - surrounding neurons have low frequency because LFP not AP.
Center/target neurons have high frequencies because AP not LFP so require high-pass filter.
SUR - pathway AP generation.
RMP - K+ channels are open, Na+ channels are closed.
Depolarization to threshold - K+ and Na+ closed.
Depolarization to AP - K+ efflux, Na+ influx.
Hyperpolarization to beneath RMP - K+ efflux, Na+ inactive.
Small depolarization to RMP - K+ open both ways, Na+ closed.
mV of RMP, threshold, peak AP
RMP = -65 mV Threshold = -40 mV AP = up to +30 mV
APs may look different because …, but since APs are always the same, this …
Because they come from different angles, this helps identifying the different neurons.
Peristimulus time histogram (PSTH) shows…
The spike counts over many trials.
Purpose of multi-unit recording (MUR) (3):
Reduce number of experimental animals.
Parallel recording tells the functioning of a system.
More and better data.
Outer ear -
Middle ear -
Inner ear -
Outer ear - amplifies sound at frequency wave important for speech perception, helps front to back localization.
Middle ear - filled with fluid and also acts as amplifier, transduces air pressure waves into fluid waves.
Inner ear - transduces fluid waves into neural activity, maintaining balance.
Power density of sound -
Cochleogram -
Power density of sound - use as function of time and frequency.
Cochleogram - use as function of time and place.
Pathway sound waves to brain.
Changes in air pressure are transmitted to changes in fluid pressure in inner ear.
Changes induce movement of basilar membrane and stereocilia of hair cells.
Movements are turned into electrical signals.
Mechanoreceptors open and permit K+ influx into hair cell.
Causing depolarization due to differences of K+ in endolymph and perilymph.
Changes in MP lead to APs and NT release - Ca2+ influx.
NTs bind to auditory nerve to brain.
Frequency mapping:
Low frequencies at apex.
High frequencies at base.
Pathway cochlea to auditory cortex.
Cochlea - cochlear nucleus - superior olivary nucleus (SON in medulla) - partly cross-over - inferior colliculus - medial geniculate nucleus of thalamus - auditory cortex in temporal lobe.
Location primary and secondary auditory cortex.
Primary superior on superior temporal gyrus, secondary inferior on superior temporal gyrus.
Superior olivary complex (2):
First interaction between information from both ears, e.g. localization.
Brainstem nuclei - extends from medulla to pons.
Medial superior olive/MSO
Sound localization by interaural time differences, < 3000 Hz.
Lateral superior olive/LSO
Sound localization by interaural intensity differences, > 3000 Hz.
MSO and LSO
Neuronal map where neurons respond most strongly when APs from two ears arrive simultaneously.
Ipsilateral excitation and simultaneously contralateral inhibition.
Inferior colliculus … cues for sound localization in space and contains …
Integrates cues and contains topographical representation of audible space.
Inferior colliculus (4):
Major integration center.
Interaction with motor system to guide behavior.
Has complete map of auditory space.
Lies in the superior caudal midbrain.
Medial geniculate nucleus of thalamus (2):
Key relay station of information to divide in cortex.
Influences direction and maintenance of attention.
Where takes higher-order processing place?
In belt areas, including speech, word recognition and comprehension.
Pitch is the … of … and … tones.
Ordered perception of high and low tones.
… and … are processed differently in the auditory cortex.
Pitch and frequency
Most information crosses over, however hemispheres process stimuli from both ipsilateral and contralateral sides. 2 advantages:
One sided brain damage causes little impact.
More processing potential.
Pathway cochlea - auditory cortex.
Cochlear nucleus - superior olivary complex - inferior colliculus - medial geniculate nucleus of thalamus - auditory cortex.
Auditory cortex is arranged tonotopically by frequency.
Apex - low frequencies > 25 Hz
Base - high frequencies > 1600 Hz
3 small bones in middle ear:
Malleus, incus, stapes.
Higher pitches are the result of … frequencies of sound waves.
Lower pitches are the result of … frequencies of sound waves.
Higher
Lower
Depending on frequency, it’s going to cause a different section of the basilar membrane to vibrate.
Easier to move … membrane than … membrane
… is … than …
… frequencies (…) need more force to vibrate.
Easier to move thinner than thicker membrane.
Apex is thicker than base.
Low frequencies (apex) need more force to vibrate - therefore more difficult to hear.
Endolymph - … K+, … mV, like…, … Na+, scala …
Perilymph - … K+, … mV, like…, … Na+, scala …
Endolymph - high K+, + 80 mV, like intracellular fluid, low Na+, scala media.
Perilymph - low K+, 0 mV, like exracellular fluid, high Na+, scala tympani.
