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Auditory Science Lab
Paediatric Cochlear Implant Program
Department of Paediatric Otolaryngology

Brief Biography

Bob Harrison has a basic training in physiology, with PhD and DSc degrees in auditory communication and neuroscience. He has carried out research with groups in England, France, the Netherlands, and most recently in Canada and the U.S.

Harrison’s early work was concerned with the peripheral auditory system, including studies on the effects of cochlear haircell damage on the transduction and coding of sound. More recently he has been exploring the functional and anatomical development of central auditory pathways, particularly the plasticity of auditory cortex. He has employed wide range of research methodologies including electrophysiology, histology, electron microscopy, behavioural psychophysics, and various neuro-imaging techniques.

In addition to laboratory research, Harrison is involved in applied/clinical research including evoked potential and otoacoustic emission studies, and behavioural studies of speech and language development in children with cochlear implants. His work has been published in over 150 full, peer-reviewed papers and numerous book chapters.

Presently Dr. Harrison is Director of Research in the Department of Otolaryngology – Head and Neck Surgery, and a Professor in the Department of Physiology. He is also a Senior Scientist at The Hospital for Sick Children, Toronto.

Research Interests

NORMAL HEARING AND AUDITORY BRAIN DEVELOPMENT: In my laboratory we use a wide range of research techniques to investigate the structure and function of the normal auditory system (asking the question: How do we normally hear?) Our studies focus both on the “mature” system, and on early developmental processes that form the auditory brain.

THE CAUSES AND CONSEQUENCES OF HEARING LOSS: We examine many different factors that can cause hearing loss, and determine what structural and functional changes occur to the inner ear and the central auditory brain.

MY RESEARCH MISSION: To increase our knowledge of the complex biological mechanisms that enable us to hear the world. With new insights, we work to prevent hearing loss and to promote normal auditory system development. For those with hearing loss, we strive to understand the exact nature of hearing deficits, and use this information towards achieving the best possible strategies for remediation and/or the planning of habilitation.

Research Activities

We investigate the structure and function of the normal auditory system using a wide range of methods. We also study the developing auditory brain, and the abnormal system.

STRUCTURE:
To examine the anatomy and/or morphology of the inner ear structures we use techniques such as standard medical imaging (CT scans), scanning electron microscopy, as well as other light transmission microscopy methods. For studies on central auditory brain structure also use various imaging methods including light and electron microscopy. These are most often combined with specialized histological preparation methods, such as corrosion casting (to look at cerebral vasculature (put in example) neural tracers (put in picture) or immuno-histochemical labeling of active nerve cells (e.g. c-Fos staining).

FUNCTION:
To probe the function of the auditory system, we employ numerous methods. With human subjects we use standard behavioural measures of hearing function, such as clinical audiogram measures and basic speech understanding tests.

We also can use a range of objective measures of hearing function such as electrophysiological evoked potentials (e.g. auditory brainstem evoked responses), or functional neuro-imaging based on magnetic signals generated by the auditory brain (MEG show diagram). To probe the function of the inner ear and peripheral auditory system, we use otoacoustic emission testing. Otoacoustic emissions (OAEs) can indicate the functional condition of cochlear haircells. We can combine OAEs with acoustic stimulation to probe some aspects of how the ear is controlled from the more central auditory brain. The methods mentioned so far are relatively non-invasive and safe to use on human subjects.

In more basic science investigations (in animal models) we use many of the techniques already outlined above. We can also use more invasive methods, such as microelectrode recordings of single neurons, or small groups of brain cells as they respond to sound stimulation. We routinely observe cells in the auditory midbrain and cortex to examine how individual cells code sound information. By recording cells from a range of positions within auditory areas we can obtain functional maps within the auditory brain. Another methodology that we have used for looking at frequency maps in auditory cortex is by direct optical imaging of changes to cerebral blood flow that results from activation of auditory neurons.

ANIMAL MODELS OF HEARING LOSS:
We can use these techniques to study how we normally hear. We are also able to determine how the auditory system fails in various types of hearing loss and deafness and explore what diseases, drugs or other factors (e.g. noise exposure) can damage the ears and cause hearing loss. After producing these "animal models" of hearing loss, we can use our functional tools to investigate the functional consequence of cochlear damage.

THE DEVELOPMENT AND PLASTICITY OF THE AUDITORY BRAIN:
We also use these research tools to follow auditory development. We can compare the function of auditory areas in the neonatal brain with the adult animal to track developmental changes. We have investigated the central auditory effects of a cochlear hearing loss in a young developing subject compared with giving the same cochlear hearing loss to a mature subject. In this way we have been able to probe the plasticity of the auditory brain and particularly how early sensory experience can influence the formation of the auditory brain.

Future Research Interests

My Auditory Science Laboratory has close collaborative links with the Cochlear Implant Research Lab and the Centre for Voice and Laryngeal Function, both in the Department of Otolaryngology. Ongoing research projects in the Auditory Science Laboratory include:

• Contralateral modulation of otoacoustic emissions using real-time DPOAE analysis.
• The development of FM coding in the auditory cortex.
• FAT4 PCP phenotype in the mouse inner ear
• Detection of auditory nerve pathology in infants using novel otoacoustic emission techniques.
• Use of immunolabelleing (c-Fos) to determine sound generated activity patterns in auditory cortex.

Current research projects in collaboration with the Cochlear Implant Research Lab include:

• The effects of bilateral cochlear implantation; benefits; age of implantation –sequential vs. simultaneous.
• Vestibular effects of childhood deafness and the impacts of cochlear implant use.
• Magnetoencephalography (MEG) imaging of auditory brain activity with bone conduction auditory input.
• Genetics of sensorineural hearing loss; including heterozygous mutations of GJB2, Pendred and CHARGE syndromes.
• Facial nerve stimulation and other side effects of electrical stimulation of the cochlear nerve.
• Cochlear implant outcome analysis in special populations including: very young infants; multiple handicaps; children with meningitis; cochlear abnormalities.

Ongoing Research in collaboration with the Centre for Voice and Laryngeal Function includes:

• Voice and speech developmental physiology in cochlea implant recipients and the signing deaf.
• Research in recurrent respiratory papillomas including establishment of a National registry and effects of vaccine application
• Post operative voice outcome using acoustic voice analysis; microdebrider vs CO2 laser effects.

External Funding

• CIHR Team Grant: The Development and Ageing of Binaural Hearing.
  5-year term, 2010-2015. RV Harrison, Team Leader. Co PIs: Lu Yang Wang, Karen Gordon, Adrian James, Vincent Lin, and Lendra Friesen.
• Canadian Institutes of Photonics Innovation (CIPI):  Osseointegration, Bone, and Soft Tissue Healing Following Ultrafast Laser Ablation in a Rat Model. 
  PIs: Nathan Jowett, Darren Kraemer, RJ Dwayne Miller, Robert V Harrison, Paul Wiseman, and Alex Mlynarek.
• CIHR Operating Grant: The programming of the neonatal auditory brain by environmental sound stimuli. 
  5-year term ends 2012. PI: RV Harrison.
• The Masonic Foundation of Ontario: New diagnostic techniques for hearing disorders.
  PI: RV Harrison.

Publications

Brown TA, Harrison RV. (2011) Neuronal responses in chinchilla auditory cortex after postnatal exposure to frequency-modulated tones. Hear Res. 275: 8-16.

Holler T, Campisi P, Allegro J, Chadha NK, Harrison RV, Papsin B, Gordon K. (2010) Abnormal voicing in children using cochlear implants. Arch Otolaryngol Head Neck Surg. 136(1):17-21.

Allegro J, Papsin B, Harrison RV, Campisi P. (2010) Acoustic analysis of voice in cochlear implant recipients with post-meningitic hearing loss. Cochlear Implants International. 11(2) 100-116.

Brown TA, Harrison RV. (2010) Postnatal development of neuronal responses to frequency-modulated tones in chinchilla auditory cortex. Brain Res. 14;1309:29-39.

Chugh BP,  Lerch JP, Yu  LX, Pienkowski  M, Harrison  RV, Henkelman  RM, Sled JG. (2009) Measurement of cerebral blood volume in mouse brain regions using micro-computed tomography.  NeuroImage 47 (2009) 1312–1318.

Brown TA, Harrison RV. (2009) Responses of neurons in chinchilla auditory cortex to frequency modulated tones. J Neurophysiol 101: 2017-2009.

Holler T, Allegro J, Chadha NK, Hawkes M, Harrison RV, Forte V, Campisi P. (2009) Voice outcomes following repeated surgical resection of laryngeal papillomata in children. Otolaryngol Head Neck Surg.141(4):522-6.

Gordon KA, Papsin BC, Harrison RV.(2007) Auditory brainstem activity and development evoked by apical versus basal cochlear implant electrode stimulation in children. Clin Neurophysiol. 118(8):1671-84.

Propst EJ, Blaser S, Stockley TL, Harrison RV, Gordon KA, Papsin BC. (2006) Temporal bone imaging in GJB2 deafness. Laryngoscope. 116(12):2178-86

Campisi P, Low A, Papsom BC, Mount RJ, Harrison RV. (2006) Multi-dimensional voice program analysis in profoundly deaf children: quantifying frequency and amplitude control. Perceptual and Motor Skills, 103: 40-50.

Gordon KA, Papsin BC, Harrison RV. (2006) An evoked potential study of the developmental time course of the auditory nerve and brainstem in children using cochlear implants. Audiol Neurotol. 2006;11(1):7-23.

Propst EJ, Papsin BC, Stockley TL, Harrison RV, Gordon KA.(2006) Auditory responses in cochlear implant users with and without GJB2 deafness. Laryngoscope. 2006 Feb;116(2):317-27.

Pienkowski M, Harrison RV. (2005) Tone responses in core versus belt auditory cortex in the developing chinchilla. J Comp Neurol. Nov 7;492(1):101-9.

Gordon KA, Papsin BC, Harrison RV. (2005) Effects of cochlear implant use on the electrically evoked middle latency response in children. Hear Res 204:78-89

Harrison RV, Gordon KA, Mount RJ (2005). Is there a critical period for cochlear implantation in congenitally deaf children? analyses of hearing and speech perception performance after implantation. Dev Psychobiol 46:252-261

James AL, Harrison RV, Pienkowski M, Dajani H,Mount RJ. (2005) Dynamics of contralateral acoustic suppression of DPOAEs measured in real time in chinchilla and human subjects. International Audiology 44:118-129

Pienkowski M, Harrison RV. (2005). Tone frequency maps and receptive fields in developing chinchilla auditory cortex. J Neurophysiol. 93: 454-466

For additional publications please visit Pub Med »»