Paracuses and Hyperacusis discusses several auditory perception disorders including hyperacusis, which is an abnormal intolerance to ordinary environmental sounds. The document reviews proposed neurophysiological models of hyperacusis including serotonin dysfunction, auditory nerve hyperactivity, and plastic changes in the central auditory system due to sensory deprivation leading to increased central gain. Research on hyperacusis is ongoing but it is strongly associated with conditions like tinnitus and migraine that may involve serotonin metabolism dysfunction.

1. Paracuses and Hyperacusis
Neurophysiological models
Prof. Dr. Amr Refai

2. Hyperacusis, mechanisms, diagnosis and therapy
(Baguley and Andersson, 2007)

3. Paracuses
• Disturbance in auditory perception (other than loss
of hearing sensitivity)
• Musicians are more sensitive to detecting it, people
infrequently complain about it (unable to recognize,
confuse, mildly irritating..)
• Hyperacusis is the most clinically encountered type

4. Paracuses
• Intensity-related phenomena
• Frequency-related phenomena
• Localizing dysfunction

5. Frequency-related phenomena
• Diplacusis:
– Double hearing (sound will have a different tone
in each ear)
– Meniere’s disease? First to disappear on
treatment?
– Cochlear otosclerosis, fenestration operations
– Potassium iodide medication, chloroform
inhalation

6. Diplacusis
• Damage to the fine tuning mechanism of the organ
of corti (outer hair cell dysfunction?)
• Lower intelligibility of speech, the benefits of
hearing aids are debatable
• PTA, speech discrimination, otoacoustic emissions
• Diplacusimetry, psychoacoustic tuning curves

7. Sound localization dysfunction
• Intensity and phase difference of sounds are
important for sound directionalization
• Time difference, the role of the auricles
• Dysstereoacusis:
– Can be seen frequently in patients with supra
tentorial lesions (central dysfunction)
– Can be the presenting symptom in vestibular
shwannoma

8. Intensity-related phenomena
• Paracusis Willisii:
– Frequently mentioned with otosclerosis
– But it is a general feature of conductive hearing
loss
– Patient’s can hear better in noisy environment
– People tend to raise their voices in noisy
environment?

9. Hyperacusis
• Unusual tolerance to ordinary environmental
sounds (Vernon, 1987)
• Consistently exaggerated or inappropriate
responses to sounds that are neither threatening
nor uncomfortably loud to a typical person (Klein et
al, 1990)

10. Other terms
• Loudness recruitment:
– Abnormal growth of loudness due to cochlear
hearing loss, and in particular OHCs dysfunction
(mechanism?)
– Sounds of moderate intensity perceived as
uncommonly loud (ABLB, SISI score?)
– Sounds of low intensity perceived as abnormally
uncomfortable (Hyperacusis)
– Cross over?

11. Other terms
• Phonophobia:
– Emphasises the emotional impact of the
sensitivity to sounds, used more in neurological
literature
– Phonophobia/photophobia accompanying
migraine attacks
– Misophonia: A term to describe disliking of
sound without the phobic element (Jestreboff,
2003)

12. Other terms
• Noise sensitivity in psychiatric disorders:
– Startle reflex in post traumatic stress disorders
– The association of noise sensitivity and
depression
– Improvement of hyperacusis after treatment of
depression in tinnitus patients?

13. Hyperacusis and tinnitus
• 9 % point prevalence (Andersson, 2002)
• 40-60% in patients attending tinnitus clinic
• In patients with primarily hyperacusis complaint,
tinnitus estimates varies between 86% (Anari et al,
1999) and 21% (Andersson et al, 2002)
• Hyperacusis as a precursor to the development of
tinnitus

14. Severe hyperacusis
• 4-5% of population have severe tinnitus
• 40% of these have significant hyperacusis
• Severe hyperacusis : 2%
– Jastreboff, 2000
– Baguley and Andersson, 2007

15. Neurophysiological models and
mechanisms
• Hyperactivity of the auditory nerve (Moore, 1995)
• 5-HT (Marriage and Barnes, 1995)
• Endogenous opioid peptides ( Sahley et al, 1996 )
• Auditory efferent dysfunction
• Plastic change leading to increased central auditory
gain

16. Serotonin ( 5-HT)
• First recognized as a powerful vasoconstrictor and
isolated by Page (1948)
• 5 Hydroxytryptamine (5-HT)
• Naturally produced in the pineal gland, and its
precursor (amino acid Tryptophan) is rich in
bananas, milk, Turkey, plums
• 90% of Serotonin in the body is in the intestine

17. 5-HT
• One role of 5-HT, is as a neurotransmitter,
regulating various functions like sleep, memory and
learning, temperature regulation, mood, appetite,
behaviour, cardiovascular function, muscle
contraction, endocrine regulation and depression.
• 5-HT released at synaptic clefts in the brain
regulate protein binding and change electrical state
of the cell, either stimulatory or inhibitory

19. 5-HT and depression ( The molecule of
happiness)
• Low serotonin levels are believed to be the cause
of many cases of mild to severe depression which
can lead to symptoms such as anxiety, apathy,
fear, feelings of worthlessness, insomnia and
fatigue. The most concrete evidence for the
connection between serotonin and depression is
the decreased concentrations of serotonin
metabolites in the cerebrospinal fluid and brain
tissues of depressed people

20. Serotonin ( 5-HT )
• Serotonergic fibres and terminal endings found
throughout central auditory pathway (Raphe Neucli)
through the medulla, pons and midbrain
• Postulated role of modulating sound perception or
determination of significance
– ( Thompson et al, 1994, Simpson and Barnes,
2000 )

21. Marriage and Barnes (1995)
The Journal of Laryngology and Otology
October 1995, Vol. 109, pp. 915-921
Neurological conditions associated with
hyperacusis:
(a) Migraine (Solomon et al, 1992).
• (b) Depression (Carmen, 1973).
• (c) Pyridoxine deficiency (Oppe, 1992).
• (d) Benzodiazepine dependence (Lader, 1984).
• (e) Musicogenic epilepsy (case study by Fujinawa
et al, 1977).

22. Neurological conditions associated with
Hyperacusis
• (f) Tay-Sach's disease or gangliosidosis type 2
• (Gordon et al, 1988; Gascon et al, 1992).
• (g) Post-traumatic stress disorder.
• (h) Chronic/post-viral fatigue syndrome (CFS/
PVFS) or myalgic encephalomyelitis (ME)
(Behan and Bakheit, 1991; Merry, 1991).

23. Hypothesis
• Many conditions associated with hyperacusis,
especially Migraine and tinnitus (probably accounts
for 90% of cases of hyperacusis), are strongly
related to dysfunction in 5-HT metabolism,
probably reduction of 5-HT activity in the forebrain

24. Problems with 5-HT hypothesis
• Non-specific ( Phillips and Carr, 1998 )
• Possible role of SSRI medication:
– A Cochrane review has found no evidence of the its
effects on tinnitus treatment
– Interest in the states, under investigation

25. Plasticity in central auditory system
• Plasticity first proposed by Ramon y Cajal
( 1852 - 1934 )
The ability of the brain to re-organize itself
• Caused by
– Reorganization following an insult (sensory
deprivation as an example)
– Adaptation and change of functions

26. The role of sensory deprivation
• Tonotopic organization through the auditory
system means that certain frequency areas
on the basilar membrane supplies certain
regions in the central auditory system with
afferent signals
• Damage to the cochlea, resulting in SNHL
will lead to loss of afferent information
leaving this specific area (frequency region)

27. Sensory deprivation theory
• Corresponding areas in the central auditory system
become starved (deprived) of sensory stimulation
• This might lead to:
– Increased level of spontaneous activity
– Plastic rearrangement of neurones leading to
abnormal firing patterns
• This can be perceived as tinnitus and hyperacusis

28. Recent PET scan findings
Seng-Ha Oh (2010)
• Pre and post cochlear implantation in pre lingual
and post lingual hearing loss
• PET looks at auditory cortical metabolism
• Wider pre-operative hypometabolism of the
auditory cortex is an indication of BETTER speech
abilities post implantation
• The more the duration of deafness the LESS the
extent of hypometabolism in the auditory cortex

29. Final thoughts
• Hyperacusis is a specific term and should not be
confused with other phenomena
• The theories of causation are still not proven,
though strong associations with cochlear damage,
tinnitus and migraine should provide a connection
to the pathophysiological mechanisms of these
conditions