📗 -> 01/21/25: Bat Echolocation 2
🎤 Vocab
❗ Unit and Larger Context
Small summary
✒️ -> Scratch Notes
Moths coevolved with bats, developing jamming ultra sound emissions to interfere with their echolocation (click-like sounds from moths).
- Pitched at the same frequency as bat sonar
Neural Correlates in Bats
Peripheral sound encoding
Acoustic Fovea
Refresher on sound
- Sound enters through the pinna
- Goes through the middle ear
- Middle ear acts as an impedance matcher, matching the impedance of liquid in ear with the air, translate information
- Use muscles to attenuate the amplitude of sound when their too loud
- Sound hits tympanic membrane, make the liquid vibrate
- Frequencies translate, go to the end
- Hit the cochlea (inner ear) in the ear, have hair cells that are specialized for the transmission of sound which transform vibration of the basilar and tectorial membrane into electrical signal
One of the characteristics of cochlea is it has the vestibular membrane, and it has different properties.
- Thicker on one end and thinner, tuned for higher frequencies
- Flatter and broader on another, tuned for lower frequencies
- Tonotopic representation
- The part of the basilar membrane that activates sends signals that it is perceiving the corresponding frequency
Specialization in Bats
Basilar Membrane thickness and width give attenuation to the harmonics of emissions
- The 2nd component of the CF2 is one of the most important for distances
Over-representation of frequencies is called the acoustic fovea
- Mustached and Horseshoe bats (CF-FM bats) have an over-representation, showing an acoustic fovea
- Little brown bat (an FM bat) does not (equal-ish representation of frequencies)
Bats (mustached bat) reduce their sensitivity to their own emission frequency
- Least sensitive: 59 kHz (frequency at which the bat emits its cry with Doppler Shift Compensation, making it so it won’t hear its own emissions as loudly)
- Most sensitive: 61 kHz
The stapes become more rigid and attenuate sound perception during emission. This prevents self deafining. Sensitivity restored when the echo is due to arrive
- During the terminal buzz, the stapes do not fully relax, reducing amplitude of echo, but close enough so it doesn’t matter
Neural Correlates
Main auditory pathway
- Sound detected in the cochlea
- Spiral ganglion neurons project to
- Cochlear nucleus (CN) then projects to:
3a. Lateral Lemniscus Nucleus (NLL), projects to
3aa. Inferior Colliculus (IC)
3b. Superior Olivary Complex (SOC), projects to
3ba. Inferior Colliculus (IC) - Inferior Colliculus (IC) then projects to
4a. Superior Colliculus
4b. Medial Geniculate Body (MGN) (one of the areas of the thalamus) - Medial Geniculate Body then projects to
- Auditory Cortex
The inferior colliculus is an important player here
Inferior Colliculus
- Midbrain auditory structure.
- Neurons are very sensitive to sound timing.
- They accurately represent the timing of pulse and echo, thus preserving delay information for the analysis by other areas.
- Neurons not sensitive to SPL (volume).
- Very narrow tuning curves.
- Maintains overrepresentation of CF2.
Auditory Cortex in CF-FM Bats
DSCF - Doppler Shifted Constant Frequency (also acoustic fovea)
CF/CF - Sensitive to combinations of constant-frequency signals
- Target velocity
- Cares about the constant frequency part of the response
FM-FM - Areas that are sensitive to combinations of frequency modulated signals - Target distance
- Only cares about the FM component of the response
DM - DorsoMedial Area - Azimuth
DSCF
Doppler Shifted Constant Frequency
-
Occupies 30% of the primary auditory cortex. The cortical counterpart of the acoustic fovea
-
Neurons are extremely selective and narrowly tuned
- Tuned for frequency and signal amplitude
-
Respond purely to the amplitude and frequency of the echo CF2, regardless of the frequency of the emitted pulse
-
Pictured as a bicycle wheel:
- Outwards along a spoke, the best frequency increases - tonotopy
- Circularly from one spoke to another, the best amplitude changes - amplitopy
-
Its sensitivity to small fluctuations in echo CF2 make it useful for flutter detection, and identifying possible prey
CF / CF Area
- CF1 / echo CF2 and CF1 / echo CF3 neurons
- Care about frequencies, not timings
- Respond to paired frequencies (combination sensitive neurons)
- Process velocity information encoded in the doppler frequency shift
🧪 -> Refresh the Info
Did you generally find the overall content understandable or compelling or relevant or not, and why, or which aspects of the reading were most novel or challenging for you and which aspects were most familiar or straightforward?)
Did a specific aspect of the reading raise questions for you or relate to other ideas and findings you’ve encountered, or are there other related issues you wish had been covered?)
🔗 -> Links
Resources
- Put useful links here
Connections
- Link all related words