Cochlear implants and brain machine interface

Nature of Sounds

Air pressure creates sounds.
A number of cycles per seconds expressed in units are called hertz.
The distance between successive compressed patches is called a cycle.

Range from 20hz to 20000,
High pitch is high frequency, low frequency= low pitch
Whilst Higher intensity means louder volume whilst lower intensity means lower volume.

Audiotory system

Peripheral auditory system

Audiotory pathway stages

Tymphanic membrane

Ossicles

Oval window

Cochlear fluid

Sensory neurone response

Sound waves

Inner Ear
-Perilymph: Fluid in the scala vestibuli and scala tympani
-Endolymph: Fluid in scala media

Pressure at the oval window pushes the perilymph into the scala vestibuli, round window membrane which bulges out.

The response of the basilar membrane is what causes the sound

Structural properties: Wider at apex, stiffness decreases from base to apex

High frequencies -> Base

Low frequencies-> Apex

Organ of Corti and associated structures as basilar membrane moves the hair cells will bend which will open up ion channels

The voltage gated channels will move the Basilar membrane upward, reticular lamina up and stereo-cilia bends outwards

Central Audiotory Processes

Cochlear Nucleus in Brainstem

Lateral Leminscus

Inferior colliculus

Thalamus- Medial Geniculate nucleus

Superior temporal gyrus

Encoding sound frequencies is through Tonotopic maps on the basilar membrane

Mechanisms of sound localisations

Interoral timing diffirence

Interoral level differences

When on ear receives the sound faster than the other sound

When one ear receives a sound first due to it being blocked by the head.

Audiotory cortex

Primary Auditory Cortex - Axons leaving the MGN(medial geniculate nucleus) project tot the auditory cortex via internal capsule in an array, Structure of A1 and secondary auditory areas: similar to corresponding visual cortex areas.

Human audiotory cortex

Hersches Gyrus

Superior temporal gyrus

Planum temporal

MGN sends to Herrshes gyrus, but also anatomical landmark of primary Audiotory cortex

Computational hub computing where and what the sound is?

Circular sulcus

Ventral-

Dorsal- where an object is in space and how to interact

Vestibular system - Importance for balance, equilibrium, posture, head,body and eye movement

Vestibular Labrynth

Otolith organs-gravity and tilt: detect changes in head angle, linear acceleration macular hair cells responding to tilt.

Semicircular canals-head rotation

Use hair cells, like audiotory system to detect changes

Cochlear Implant technology

Inner Components

External Components

Microphone

Battery pack

Sound processor

Transmitter

Reciever

Electrode

Sound like sparse input

This is due to the loss of hair cells

The electrode is usually inserted through the round window or through a hole drilled nearby (cochleostomy) in the scala tympani.

Social impats

Cochlear: Social Impact

CL recipients achieves 9% of sentence recognition, recognition of 55% of monosyllabic words

Improves over time up to 1 year to interpret the sparse input

Bilateral allows for sound localisations

Types of Deafness

Prelingual -before you acquire a language, Delaying Cochlear implants delays language function

Post-lingual At a later age - showing linkage between hearing loss and dementia

Improvements in CIs

BIlateral localisaiton

Combined electrical and acoustic stimulation for patients with residual hearings

Adaptive signal processing (noisy vs quiet environment)

Remaining gaps in prosthetic hearing

Some users have very poor speech perception

Speech recognition is much more difficult for all CL recipients in adverse noisy hearing conditions

Perception of music mains leusive

Tonal language difficulties

When there is a sensorineural hearing loss (loss of inner hair cells) but the auditory nerve is largely in tack
Brainstem implant- appropriate when there is degeneration of the audiotory nerve

Scientific IMpacts

Increased understanding of the nature of sensitive period for language acquisition.
The earlier the better for language outcomes
Still get benefits of CIs for prelingually deaf up to 9 years age

Commercialism/History

Cochlear LTd (AUSTRALIA)

Bionic Eyes

Optic nerve stimulation

Retinitis PIgemntosa

Macula degeneration

Visual Cortex sitmiation

Diabetic reinopathy,glaucoma

BMI use brains signals

Use brain signal features related responses Oscillation that correspond to voluntary though to bypass disabled portions of the nervous system eg the spinal cord and coonnects directly to physical devices for communication or locomtion

BCI invasive (surgically implanted electrode or grids or non invasive EEG,MEG,FMRI,fNIRS assistive or rehabilitation

Motor imagery the same brain are activated using imaginative actions when trying to perform a task.

Subdural electrodes over motor cortex patient can control computers

Advanced bionics (USA)

MED-EL Austria (AUSTRIA)

Nurtrin (CHINA)

Graeme clarke (Australia) and William House( USA) made the pioneering studies in 1960 and 1970s

Initial resistance from the CL and signing def community (cultural assimilation)- to young to consent.