1 - Anatomy, connections, and development
Auditory physiology is a highly technical and
specialized field, and the neuroanatomy and
neurochemistry are complex. It might be fruitful to try
to persuade specialists in the fields of normal and
disordered hearing to take an interest in the auditory
problems of children with autism. That children with
autism have impairments in hearing is not universally
accepted, but a significant prevalence of hearing loss
and (perhaps more interesting) hyperacusis have
been reported [1, 2].
Hyperacusis suggests loss of inhibitory neuro-
transmission, which might be of interest to
researchers investigating inhibition in the auditory
system [3-5]. Conversely thd growing body of
literature on inhibition should be of importance to
researchers trying to understand why children with
autism are not learning to speak, by ear, the way that
normal children do. What features of speech might be
masked by persistence of sounds not relegated to
background by inhibition quickly following onset of
sounds coming in rapid succession?
What follows is just a brief overview with a few
excerpts from the literature on auditory anatomy and
function that might have some bearing on the
problems of children with autism. The auditory system
includes nuclei and nerve tracts from the ears through
lower brainstem nuclei to midbrain, thalamus, and
temporal lobes of the cerebral cortex. Figure 11
depicts these components.
Interconnections with neurons in the reticular
formation and superior colliculi are involved in reflex
eye movements and turning of the head in response
to sounds of interest. These interconnections indicate
the importance of hearing even at the subcortical level
as part of a total-body sense of orientation and
response capability [6-8].
Sound stimuli are transmitted from the ears to the
cerebral cortex via the cochlear nerve to the cochlear
nucleus, then onward to the trapezoid body, and
superior olive in the lower brainstem. The lateral
lemniscal nerve tracts connect the superior olive to
the inferior colliculus in the midbrain. The brachium of
the inferior colliculus transmits the signals to the
medial geniculate body in the thalamus, and the
auditory radiations from thalamus to the temporal
lobes. Investigations of single neuron electrical
activity and neurotransmitter interactions are
revealing that each way-station performs specific
functions in the processing of sound signals;
otherwise a single direct bundle of nerve axons from
ear to temporal lobes would suffice.
In addition to transmission from ears to cortex, nerve
pathways from the cerebral cortex also send efferent
signals back to brainstem nuclei, which in turn send
signals to lower brainstem nuclei [9-13]. Manley and
Köppl (1998) described evolutionary stages that
provide innervation of the hair cells of the ear from
higher centers, and how associations between
auditory and facial motor neurons may have evolved [1
4]. Interruption of neural circuits between auditory,
facial, and oculomotor control centers may be relevant
to poor eye contact and lack of facial expression
characteristic of autistic children.
As discussed above (in chapters 8 and xx) Yakovlev
and Lecours (1967) found in the human fetus that
myelinization of nerve tracts begins in the brainstem,
and myelin is first evident in the inferior colliculus;
figure 6 is one of the photographs from their report
[15]. The research of Yakovlev and Lecours
confirmed earlier findings of Langworthy (1933),
whose data is shown in figure 7 [16].
Moore et al. (1995) again determined that myelin
formation takes place in the auditory system between
the 26th and 29th weeks of gestation and verified that
response to sound first appears during this period of
development [17]. Sano et al. (2007) have provided
data on myelin maturation measured on MRI scans
that indicate a longer (11 to 18 weeks) span of time
from early to complete functional maturation of myelin
in the auditory pathway [18]. Use of MRI to determine
maturation and function in cases of deafness and
developmental language disorders should soon
accelerate understanding of auditory dysfunction in
young children.
Early maturing brainstem pathways may have a
trophic influence on later developing target regions of
the cerebral cortex. For example, Kungel and Friauf
(1995) identified the transient presence of the peptide
somatostatin during early development in laboratory
rats [19]. Somatostatin may be one of several trophic
transmitters within the brainstem auditory system
important for development of later maturing language
circuits in the temporal lobes [20].
In progress
Auditory physiology is a highly technical and
specialized field, and the neuroanatomy and
neurochemistry are complex. It might be fruitful to try
to persuade specialists in the fields of normal and
disordered hearing to take an interest in the auditory
problems of children with autism. That children with
autism have impairments in hearing is not universally
accepted, but a significant prevalence of hearing loss
and (perhaps more interesting) hyperacusis have
been reported [1, 2].
Hyperacusis suggests loss of inhibitory neuro-
transmission, which might be of interest to
researchers investigating inhibition in the auditory
system [3-5]. Conversely thd growing body of
literature on inhibition should be of importance to
researchers trying to understand why children with
autism are not learning to speak, by ear, the way that
normal children do. What features of speech might be
masked by persistence of sounds not relegated to
background by inhibition quickly following onset of
sounds coming in rapid succession?
What follows is just a brief overview with a few
excerpts from the literature on auditory anatomy and
function that might have some bearing on the
problems of children with autism. The auditory system
includes nuclei and nerve tracts from the ears through
lower brainstem nuclei to midbrain, thalamus, and
temporal lobes of the cerebral cortex. Figure 11
depicts these components.
Interconnections with neurons in the reticular
formation and superior colliculi are involved in reflex
eye movements and turning of the head in response
to sounds of interest. These interconnections indicate
the importance of hearing even at the subcortical level
as part of a total-body sense of orientation and
response capability [6-8].
Sound stimuli are transmitted from the ears to the
cerebral cortex via the cochlear nerve to the cochlear
nucleus, then onward to the trapezoid body, and
superior olive in the lower brainstem. The lateral
lemniscal nerve tracts connect the superior olive to
the inferior colliculus in the midbrain. The brachium of
the inferior colliculus transmits the signals to the
medial geniculate body in the thalamus, and the
auditory radiations from thalamus to the temporal
lobes. Investigations of single neuron electrical
activity and neurotransmitter interactions are
revealing that each way-station performs specific
functions in the processing of sound signals;
otherwise a single direct bundle of nerve axons from
ear to temporal lobes would suffice.
In addition to transmission from ears to cortex, nerve
pathways from the cerebral cortex also send efferent
signals back to brainstem nuclei, which in turn send
signals to lower brainstem nuclei [9-13]. Manley and
Köppl (1998) described evolutionary stages that
provide innervation of the hair cells of the ear from
higher centers, and how associations between
auditory and facial motor neurons may have evolved [1
4]. Interruption of neural circuits between auditory,
facial, and oculomotor control centers may be relevant
to poor eye contact and lack of facial expression
characteristic of autistic children.
As discussed above (in chapters 8 and xx) Yakovlev
and Lecours (1967) found in the human fetus that
myelinization of nerve tracts begins in the brainstem,
and myelin is first evident in the inferior colliculus;
figure 6 is one of the photographs from their report
[15]. The research of Yakovlev and Lecours
confirmed earlier findings of Langworthy (1933),
whose data is shown in figure 7 [16].
Moore et al. (1995) again determined that myelin
formation takes place in the auditory system between
the 26th and 29th weeks of gestation and verified that
response to sound first appears during this period of
development [17]. Sano et al. (2007) have provided
data on myelin maturation measured on MRI scans
that indicate a longer (11 to 18 weeks) span of time
from early to complete functional maturation of myelin
in the auditory pathway [18]. Use of MRI to determine
maturation and function in cases of deafness and
developmental language disorders should soon
accelerate understanding of auditory dysfunction in
young children.
Early maturing brainstem pathways may have a
trophic influence on later developing target regions of
the cerebral cortex. For example, Kungel and Friauf
(1995) identified the transient presence of the peptide
somatostatin during early development in laboratory
rats [19]. Somatostatin may be one of several trophic
transmitters within the brainstem auditory system
important for development of later maturing language
circuits in the temporal lobes [20].
In progress
| Figure 6 - From Yakovlev & Lecours (1967) showing prominent myelination in the inferior colliculus (ICOL) at 25 gestational weeks (below) and 29 gestational weeks (right). |
| Figure 7 - From Langworthy (1933): Myelination of the acoustic colliculus at 28 weeks gestation |
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| Figure 11 - Diagram of the auditory system. |
- Khalfa S et al. (2004)
Increased perception of
loudness in autism. - Rosenhall U et al. (1999)
Autism and hearing loss. - Campbell LE et al. (2007)
Primary and secondary
neural networks of auditory
prepulse inhibition: a
functional magnetic
resonance imaging study of
sensorimotor gating of the
human acoustic startle
response. - Gillespie DC et al. (2005)
Inhibitory synapses in the
developing auditory system
are glutamatergic. - Bauer EE et al. (2000), Klug
A, Pollak GD. Features of
contralaterally evoked
inhibition in the inferior
colliculus. - Coleman JR, Clerici WJ
(1987) Sources of
projections to subdivisions
of the inferior colliculus in
the rat. - Sparks DL (1989) The
neural encoding of the
location of targets for
saccadic eye movements. - Garcia Del Cano G, et al.
(2006) Organization and
origin of the connection from
the inferior to the superior
colliculi in the rat. - Coomes Peterson D,
Schofield BR (2007)
Projections from auditory
cortex contact ascending
pathways that originate in
the superior olive and
inferior colliculus. - Winer JA, Lee CC (2007)
The distributed auditory
cortex. - Darrow KN et al. (2006)
Cochlear efferent feedback
balances interaural
sensitivity. - Schofield BR, Coomes DL
(2006) Pathways from
auditory cortex to the
cochlear nucleus in guinea
pigs. - Winer JA (2006) Decoding
the auditory corticofugal
systems. - Manley GA, Köppl C (1998).
Phylogenetic development of
the cochlea and its
innervation. - Yakovlev PI, Lecours A-R
(1967) The myelogenetic
cycles of regional maturation
of the brain. - Langworthy OR (1933)
Development of behavior
patterns and myelinization of
the nervous system in the
human fetus and infant. - Moore JK et al. (1995). Time
course of axonal myelination
in the human brainstem
auditory pathway. - Sano M et al. (2007).Early
myelination patterns in the
brainstem auditory nuclei
and pathway: MRI evaluation
study. - Kungel M, Friauf E (1995).
Somatostatin and leu-
enkephalin in the rat auditory
brainstem during fetal and
postnatal development. - Kungel M et al. (1997)
Influence of the neuro-
peptide somatostatin on the
development of dendritic
morphology: a cysteamine-
depletion study in the rat
auditory brainstem.
- Myelination,
- Myelination,
| Diagram of the auditory system |
Yakovlev & Lecours, 1967
Langworthy, 1933
- Khalfa S, Bruneau N, Roge B, Georgieff N, Veuillet E, Adrien JL, Barthelemy C, Collet L.
Increased perception of loudness in autism. Hear Res. 2004 Dec;198(1-2):87-92. - Rosenhall U, Nordin V, Sandstrom M, Ahlsen G, Gillberg C. Autism and hearing loss. J
Autism Dev Disord. 1999 Oct;29(5):349-57. - Campbell LE, Hughes M, Budd TW, Cooper G, Fulham WR, Karayanidis F, Hanlon MC,
Stojanov W, Johnston P, Case V, Schall U. Primary and secondary neural networks of
auditory prepulse inhibition: a functional magnetic resonance imaging study of sensorimotor
gating of the human acoustic startle response. Eur J Neurosci. 2007 Oct;26(8):2327-33. - Gillespie DC, Kim G, Kandler K. Inhibitory synapses in the developing auditory system are
glutamatergic. Nat Neurosci. 2005 Mar;8(3):332-8. - Bauer EE, Klug A, Pollak GD. Features of contralaterally evoked inhibition in the inferior
colliculus. Hear Res. 2000 Mar;141(1-2):80-96. - Coleman JR, Clerici WJ. Sources of projections to subdivisions of the inferior colliculus in the
rat. J Comp Neurol. 1987 Aug 8;262(2):215-26. - Sparks DL.The neural encoding of the location of targets for saccadic eye movements. J Exp
Biol. 1989 Sep;146:195-207. - Garcia Del Cano G, Gerrikagoitia I, Alonso-Cabria A, Martinez-Millan L. Organization and
origin of the connection from the inferior to the superior colliculi in the rat. J Comp Neurol.
2006 Dec 10;499(5):716-31. - Coomes Peterson D, Schofield BR. Projections from auditory cortex contact ascending
pathways that originate in the superior olive and inferior colliculus. Hear Res. 2007 Oct;232(1-
2):67-77. - Winer JA, Lee CC. The distributed auditory cortex. Hear Res. 2007 Jul;229(1-2):3-13.
- Darrow KN, Maison SF, Liberman MC. Cochlear efferent feedback balances interaural
sensitivity. Nat Neurosci. 2006 Dec;9(12):1474-6. - Schofield BR, Coomes DL. Pathways from auditory cortex to the cochlear nucleus in guinea
pigs. Hear Res. 2006 Jun-Jul;216-217:81-9. - Winer JA. Decoding the auditory corticofugal systems. Hear Res. 2006 Feb;212(1-2):1-8.
- Manley GA, Köppl C (1998). Phylogenetic development of the cochlea and its innervation.
Current Opinion In Neurobiology 8:468-474. - Yakovlev PI and Lecours A-R (1967) The myelogenetic cycles of regional maturation of the
brain. In A. Minkowski (Ed.), Regional Development of the Brain in Early Life (pp. 3-70).
Oxford: Blackwell Scientific Publications. - Langworthy OR (1933) Development of behavior patterns and myelinization of the nervous
system in the human fetus and infant. Contributions to Embryology, no. 139 24:1-57. - Moore JK, Perazzo LM, Braun A (1995). Time course of axonal myelination in the human
brainstem auditory pathway. Hearing Research 87:21-31, 91:208-209. - Sano M, Kaga K, Kuan CC, Ino K, Mima K.Early myelination patterns in the brainstem auditory
nuclei and pathway: MRI evaluation study. Int J Pediatr Otorhinolaryngol. 2007 Jul;71(7):1105-
15. - Kungel M and Friauf E (1995). Somatostatin and leu-enkephalin in the rat auditory brainstem
during fetal and postnatal development. Anatomy and Embryology, 191, 425-443. - Kungel M, Piechotta K, Rietzel HJ, Friauf E. Influence of the neuropeptide somatostatin on the
development of dendritic morphology: a cysteamine-depletion study in the rat auditory
brainstem. Brain Res Dev Brain Res. 1997 Jul 18;101(1-2):107-14.
In progress