Bone conduction auditory brainstem response

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Bone conduction auditory brainstem response
Medical diagnostics
Purposerecords neural response from EEG

Bone-conduction auditory brainstem response or BCABR is a type of auditory evoked response that records neural response from EEG with stimulus transmitted through bone conduction.

Bone conduction conduction of sound to the inner ear through the bones of the skull

Bone conduction is the conduction of sound to the inner ear through the bones of the skull, allowing the user to consume audio content without blocking the ear canal. Bone conduction transmission can be used with individuals with normal or impaired hearing.

Contents

Types of bone conduction

Vibration of the skull results in auditory sensation. This is a way to somewhat bypass the outer and middle ears to stimulate the cochlea. Von Bekesy is credited with the discovery that at the level of the cochlea, phase shifted bone-conduction signals cancel out air conduction signals. Bone-conduction works because all of the bones of the skull are connected, including the temporal bone, which in turn stimulates the cochlea. Barany (1938) and Herzog & Krainz (1926) were some of the first researchers to examine the different components of bone-conduction hearing. Tonndorf (1968) found that there are three different forces that contribute to the forces needed to stimulate the cochlea: Distortional, Inertial (Ossicular), and External canal (Osseotympanic) [1]

Outer ear outer part of ear

The outer ear, external ear, or auris externa is the external portion of the ear, which consists of the auricle and the ear canal . It gathers sound energy and focuses it on the eardrum.

Cochlea organ of the inner ear

The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2 turns(full) and a 3/4(3 quarters) turn around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory organ of hearing, which is distributed along the partition separating fluid chambers in the coiled tapered tube of the cochlea.

Temporal bone bones situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum

The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex.

Distortional bone-conduction

As vibrations compress the bones of the skull, pressure is put on the otic capsule and the membranous labyrinth. This then compresses the scala vestibule into the basilar membrane in the direction toward the scala tympani. A traveling wave is created similar to that created by air conduction signals.

Membranous labyrinth system of tubes and chambers in the inner ear

The membranous labyrinth is a collection of fluid filled tubes and chambers which contain the receptors for the senses of equilibrium and hearing. It is lodged within the bony labyrinth in the inner ear and has the same general form; it is, however, considerably smaller and is partly separated from the bony walls by a quantity of fluid, the perilymph.

Basilar membrane

The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani.

Inertial bone-conduction

The ossicles are suspended in the head and loosely coupled to the skull. When the head moves, the ossicles move out of phase with the head, but still follow the same cyclic motion. This causes the stapes to move in and out of the oval window. When vibrations come from the mastoid, inertial bone-conduction is greatest below 800 Hz. Putting the bone vibrator on the forehead instead of the mastoid does not significantly create this affect.

Ossicles bone

The ossicles are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss. The term "ossicle" literally means "tiny bone". Though the term may refer to any small bone throughout the body, it typically refers to the malleus, incus, and stapes of the middle ear.

Stapes bone of the middle ear

The stapes or stirrup is a bone in the middle ear of humans and other mammals which is involved in the conduction of sound vibrations to the inner ear. The stirrup-shaped small bone is on and transmits these to the oval window, medially. The stapes is the smallest and lightest named bone in the human body, and is so-called because of its resemblance to a stirrup.

Osseotympanic bone-conduction

This type of bone-conduction also involves low frequencies. As a bone vibrator vibrates the skull, the bone and cartilage of the external ear receives energy, most of which escapes the unoccluded ear. Some of this energy hits the tympanic membrane and combines with inertial bone-conduction, stimulating the inner ear. An example of this occurs when you close your ears and speak- your voice appears to be much lower in frequency.

Bone-conduction ABR

Bone-conduction auditory brainstem response (BCABR) are similar to air conduction auditory brainstem responses, with the main difference being that the signal is transmitted via bone-conduction instead of air. The goal of bone ABR is to estimate cochlear function and to help identify the type of hearing loss present. [2] Responses to air and bone-conduction ABRs are compared (for the same intensity and stimuli).

The auditory brainstem response (ABR) is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The measured recording is a series of six to seven vertex positive waves of which I through V are evaluated. These waves, labeled with Roman numerals in Jewett and Williston convention, occur in the first 10 milliseconds after onset of an auditory stimulus. The ABR is considered an exogenous response because it is dependent upon external factors.

Stimulus (physiology) in physiology, a detectable change in the internal or external environment

In physiology, a stimulus is a detectable change in the physical or chemical structure of an organism's internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity. When a stimulus is applied to a sensory receptor, it normally elicits or influences a reflex via stimulus transduction. These sensory receptors can receive information from outside the body, as in touch receptors found in the skin or light receptors in the eye, as well as from inside the body, as in chemoreceptors and mechanoreceptors. An internal stimulus is often the first component of a homeostatic control system. External stimuli are capable of producing systemic responses throughout the body, as in the fight-or-flight response. In order for a stimulus to be detected with high probability, its level must exceed the absolute threshold; if a signal does reach threshold, the information is transmitted to the central nervous system (CNS), where it is integrated and a decision on how to react is made. Although stimuli commonly cause the body to respond, it is the CNS that finally determines whether a signal causes a reaction or not.

Techniques and results for bone-conduction auditory brainstem responses are presented in a review chapter by Stapells, [3] as well as in a detailed assessment protocol by the British Columbia Early Hearing Program (BCEHP). [4]

When is BCABR needed?

Any infant showing elevated ABR thresholds to air-conduction stimuli should be tested using bone-conduction stimuli. Atresia, microtia, otitis media and other outer/middle ear abnormalities, as well as infants with sensorineural hearing loss, will require the use of bone-conduction ABR testing. Infants who have a considerable amount of amniotic fluid in their middle ear space may need to be tested with BCABR. This fluid usually disappears by 48 hours after birth.

Problems with BCABR

It is very common for there to be a large amount of artifact while using bone-conduction ABR. This is especially true at high intensities (~50 dB nHL) and at earlier waves (i.e. Wave I). To avoid stimulus artifact, it is recommended that the bone oscillator be placed high on the temporal bone and that the inverting electrode is placed on the earlobe, mastoid, or nape of the neck. Using an alternating phase stimuli should be used to reduce artifact. Since the output of most bone oscillators is around 45 to 55 dB nHL, it becomes difficult to distinguish between sensorineural or mixed hearing losses when the losses by bone exceed this number. This output limitation of the bone oscillator is a drawback.

BCABR responses

With Bone ABR, the waves are typically more rounded that with traditional auditory brainstem response. The maximum output for bone is around 50 dB nHL and should look similar to the 50 dB HL response of air conduction for people with normal hearing or with a mild SNHL. With conductive hearing losses, the latencies for air are shifted when compared to the latencies of bone-conduction.

Mauldin & Jerger (1979) found that for adults, the Wave V latencies derived from bone-conduction ABR are approximately 0.5 ms longer than the same intensity level of air conduction. [5] For infants, Wave V latencies for bone-conduction clicks are shorter than the air conduction clicks. [6] These differences can be attributed to changes to the skull due to aging.

BCABR with tone bursts

As with air-conduction stimuli, thresholds for bone-conduction stimuli should be obtained using tone burst stimuli Stapells is one researcher who reported on the accuracy of using tone bursts with BC ABR to estimate cochlear hearing sensitivity. Stapells and Ruben, in 1989, demonstrated bone-conduction tone burst ABRs in infants with conductive hearing loss. [7] Hatton, Janssen and Stapells (2012) present bone-conduction tone burst ABR results in infants with normal bone-conduction thresholds or sensorineural hearing loss. [8] BC ABR methods are described in 2010 review chapter by Stapells. [9]

Physiology

Wegel and Lane found that low-frequencies masked high-frequencies better than the highs mask the lows. This is explained by von Bekesy's findings that the cochlea has an asymmetrical filter function effect. This asymmetry and higher travelling wave velocity at the base explains why the ABR is biased towards the high frequencies. For a low-frequency tone burst, the travelling wave velocity is greatest at the base than at the apex. For low frequency tone bursts, the displacement is largest in the apex. The neural response is synchronous only over a short distance of the apex. The response is broader due to lack of neural synchrony. High intensity tone bursts stimulate more of the basal areas. Tone burst masking techniques have been developed to overcome this upward spread of masking.

Click stimuli have no frequency specificity, thus it is not possible to know which frequencies specifically contribute to a click threshold. tonal stimuli are required to obtain frequency-specific thresholds. An ideal tone burst has energy at a pure-tone frequency (e.g. 2000 Hz) regardless of the intensity. This tone burst would stimulate the corresponding area on the basilar membrane. However, if a tone burst is too short in duration, it could cause spectral splatter and lose its frequency selectivity. Tone bursts approximately 5 cycles in duration appear to be acceptable.

Nevertheless, due to normal cochlear function, any tonal stimulus (even continuous long-duration tones), presented at high intensity levels, will result in stimulation of higher frequency cochlear regions ("upward spread of excitation").

Polarity

Stapells recommends using alternating polarity to reduce stimulus artifact, especially with tone burst stimuli. (Contrary to some suggestions, there is no evidence that thresholds for single-polarity tone bursts (e.g., rarefaction) are better than those to alternating polarity. [10]

For some high intensity tone bursts, especially 500–1000 Hz, single (e.g., rarefaction) polarity results in very large amplitude stimulus artifact, making it difficult to distinguish waves from artifact. Using an alternating polarity helps to revert the ABR back to typical looking waveforms.

Rarefaction polarity is recommended for clicks.

Effectiveness

See also

Related Research Articles

Vestibulocochlear nerve

The vestibulocochlear nerve, known as the eighth cranial nerve, transmits sound and equilibrium (balance) information from the inner ear to the brain.

Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.

Acoustic reflex

The acoustic reflex is an involuntary muscle contraction that occurs in the middle ear in response to high-intensity sound stimuli or when the person starts to vocalize.

Conductive hearing loss

Conductive hearing loss (CHL) occurs when there is a problem transferring sound waves anywhere along the pathway through the outer ear, tympanic membrane (eardrum), or middle ear (ossicles). If a conductive hearing loss occurs in conjunction with a sensorineural hearing loss, it is referred to as a mixed hearing loss. Depending upon the severity and nature of the conductive loss, this type of hearing impairment can often be treated with surgical intervention or pharmaceuticals to partially or, in some cases, fully restore hearing acuity to within normal range. However, cases of permanent or chronic conductive hearing loss may require other treatment modalities such as hearing aid devices to improve detection of sound and speech perception.

Sensorineural hearing loss human disease

Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ or the vestibulocochlear nerve. SNHL accounts for about 90% of reported hearing loss. SNHL is generally permanent and can be mild, moderate, severe, profound, or total. Various other descriptors can be used depending on the shape of the audiogram, such as high frequency, low frequency, U-shaped, notched, peaked, or flat.

An otoacoustic emission (OAE) is a sound which is generated from within the inner ear. Having been predicted by Thomas Gold in 1948, its existence was first demonstrated experimentally by David Kemp in 1978 and otoacoustic emissions have since been shown to arise through a number of different cellular and mechanical causes within the inner ear. Studies have shown that OAEs disappear after the inner ear has been damaged, so OAEs are often used in the laboratory and the clinic as a measure of inner ear health.

Audiometry is a branch of audiology and the science of measuring hearing acuity for variations in sound intensity and pitch and for tonal purity, involving thresholds and differing frequencies. Typically, audiometric tests determine a subject's hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or distinguish speech from background noise. Acoustic reflex and otoacoustic emissions may also be measured. Results of audiometric tests are used to diagnose hearing loss or diseases of the ear, and often make use of an audiogram.

Auditory neuropathy (AN) is a variety of hearing loss in which the outer hair cells within the cochlea are present and functional, but sound information is not faithfully transmitted to the auditory nerve and brain properly. Also known as auditory neuropathy/auditory dys-synchrony (AN/AD) or auditory neuropathy spectrum disorder (ANSD).

Presbycusis, or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive and irreversible bilateral symmetrical age-related sensorineural hearing loss resulting from degeneration of the cochlea or associated structures of the inner ear or auditory nerves. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging is not presbycusis, although differentiating the individual effects of distinct causes of hearing loss can be difficult.

In audiology and psychoacoustics the concept of critical bands, introduced by Harvey Fletcher in 1933 and refined in 1940, describes the frequency bandwidth of the "auditory filter" created by the cochlea, the sense organ of hearing within the inner ear. Roughly, the critical band is the band of audio frequencies within which a second tone will interfere with the perception of the first tone by auditory masking.

Audiogram type of graph showing audiometer results

An audiogram is a graph that shows the audible threshold for standardized frequencies as measured by an audiometer. The Y axis represents intensity measured in decibels and the X axis represents frequency measured in hertz. The threshold of hearing is plotted relative to a standardised curve that represents 'normal' hearing, in dB(HL). They are not the same as equal-loudness contours, which are a set of curves representing equal loudness at different levels, as well as at the threshold of hearing, in absolute terms measured in dB SPL.

Interaural time difference

The interaural time difference when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localization of sounds, as it provides a cue to the direction or angle of the sound source from the head. If a signal arrives at the head from one side, the signal has further to travel to reach the far ear than the near ear. This pathlength difference results in a time difference between the sound's arrivals at the ears, which is detected and aids the process of identifying the direction of sound source.

Binaural fusion or binaural integration is a cognitive process that involves the "fusion" of different auditory information presented binaurally, or to each ear. In humans, this process is essential in understanding speech as one ear may pick up more information about the speech stimuli than the other.

Pure tone audiometry

Pure tone audiometry (PTA) is the key hearing test used to identify hearing threshold levels of an individual, enabling determination of the degree, type and configuration of a hearing loss and thus providing a basis for diagnosis and management. PTA is a subjective, behavioural measurement of a hearing threshold, as it relies on patient responses to pure tone stimuli. Therefore, PTA is only used on adults and children old enough to cooperate with the test procedure. As with most clinical tests, calibration of the test environment, the equipment and the stimuli to ISO standards is needed before testing proceeds. PTA only measures audibility thresholds, rather than other aspects of hearing such as sound localization and speech recognition. However, there are benefits to using PTA over other forms of hearing test, such as click auditory brainstem response (ABR). PTA provides ear specific thresholds, and uses frequency specific pure tones to give place specific responses, so that the configuration of a hearing loss can be identified. As PTA uses both air and bone conduction audiometry, the type of loss can also be identified via the air-bone gap. Although PTA has many clinical benefits, it is not perfect at identifying all losses, such as ‘dead regions’ of the cochlea and neuropathies such as auditory processing disorder (APD). This raises the question of whether or not audiograms accurately predict someone's perceived degree of disability.

Cortical deafness agnosia that is a loss of the ability to perceive any auditory information but whose hearing is intact

Cortical deafness is a rare form of sensorineural hearing loss caused by damage to the primary auditory cortex. Cortical deafness is an auditory disorder where the patient is unable to hear sounds but has no apparent damage to the anatomy of the ear, which can be thought of as the combination of auditory verbal agnosia and auditory agnosia. Patients with cortical deafness cannot hear any sounds, that is, they are not aware of sounds including non-speech, voices, and speech sounds. Although patients appear and feel completely deaf, they can still exhibit some reflex responses such as turning their head towards a loud sound.

The olivocochlear system is a component of the auditory system involved with the descending control of the cochlea. Its nerve fibres, the olivocochlear bundle (OCB), form part of the vestibulocochlear nerve, and project from the superior olivary complex in the brainstem (pons) to the cochlea.

Hearing sensory perception of sound by living organisms

Hearing, or auditory perception, is the ability to perceive sounds by detecting vibrations, changes in the pressure of the surrounding medium through time, through an organ such as the ear. The academic field concerned with hearing is auditory science.

Electrocochleography is a technique of recording electrical potentials generated in the inner ear and auditory nerve in response to sound stimulation, using an electrode placed in the ear canal or tympanic membrane. The test is performed by an otologist or audiologist with specialized training, and is used for detection of elevated inner ear pressure or for the testing and monitoring of inner ear and auditory nerve function during surgery.

The frequency following response (FFR), also referred to as frequency following potential (FFP) or envelope following response (EFR), is an evoked potential generated by periodic or nearly-periodic auditory stimuli. Part of the auditory brainstem response (ABR), the FFR reflects sustained neural activity integrated over a population of neural elements: "the brainstem response...can be divided into transient and sustained portions, namely the onset response and the frequency-following response (FFR)". It is often phase-locked to the individual cycles of the stimulus waveform and/or the envelope of the periodic stimuli. It has not been well studied with respect to its clinical utility, although it can be used as part of a test battery for helping to diagnose auditory neuropathy. This may be in conjunction with, or as a replacement for, otoacoustic emissions.

References

  1. ↑ Katz, J. (2002). Handbook of Clinical Audiology. Philadelphia. Lippincott Williams & Wilkins
  2. ↑ Roeser, R. (2000). Audiology Diagnosis. New York, NY. Thieme Medical Publishers
  3. ↑ Stapells, D.R. (2010). Frequency-specific ABR and ASSR threshold assessment in young infants. In Seewald R.C. & Bamford, J (Eds.). A Sound Foundation Through Early Amplification 2010. Stäfa: Phonak AG. Pp. 67-105
  4. ↑ British Columbia Early Hearing Program (BCEHP) (2012), BCEHP Audiology Assessment Protocol, http://www.phsa.ca/AgenciesAndServices/Services/BCEarlyHearing/ForProfes-sionals/Resources/Protocols-Standards.htm%5B%5D.
  5. ↑ Mauldin, L. & Jerger, J. (1979). Auditory brain stem evoked responses to bone-conducted signals. Archives of Otolaryngology; 105, 656-661.
  6. ↑ Yang et al (1987). A developmental study of bone-conduction auditory brain stem response in infants. Ear & Hearing; 8, 4.
  7. ↑ Stapells, D.R., & Ruben, R.J. Auditory brainstem responses to bone-conducted tones in infants. Annals of Otology, Rhinology and Laryngology, 1989, 98, 941-949.
  8. ↑ Hatton JL, Janssen RM, Stapells, DR. Auditory brainstem responses to bone-conducted brief tones in young children with conductive or sensorineural hearing loss. International Journal of Otolaryngology 01/2012; 2012:284864. DOI: 10.1155/2012/284864
  9. ↑ Stapells, D.R. (2010). Frequency-specific ABR and ASSR threshold assessment in young infants. In Seewald R.C. & Bamford, J (Eds.). A Sound Foundation Through Early Amplification 2010. Stäfa: Phonak AG. Pp. 67-105
  10. ↑ Stapells, D.R. (2010). Frequency-specific ABR and ASSR threshold assessment in young infants. In Seewald R.C. & Bamford, J (Eds.). A Sound Foundation Through Early Amplification 2010. Stäfa: Phonak AG. Pp. 67-105
  11. ↑ Hall, J. W. (1992). Handbook of auditory evoked responses. Boston, MA: Allyn & Bacon
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