Processing of sensory information in the central nervous system enables conscious perception of our environment and communication with the external world. It takes approximately 200 milliseconds until we become aware of a stimulus, which is received by our peripheral sensory organs. During this short interval of time the brain performs in parallel an incredible amount of complicated signal processing tasks: The stimulus of interest is segregated from background information, detailed information belonging to one object are integrated into an unified entity, information are integrated over time for improving the signal to noise contrast, sensory information are stored in short term memory and continuously compared with our internal knowledge about the environment, and many more sophisticated analyses are performed. We can control or modulate intentionally most of central sensory processing through directing the focus of attention and select consciously the stimulus of interest.

Sensory processing and perception enable meaningful cognition and action and vice versa, deficits in central sensory processing have detrimental effects on cognitive abilities. Conditions of impaired central sensory processing occur over the full lifespan. For example, central processing disorders during development and adolescence result in learning disabilities, a traumatic brain injury may impair central sensory processing and has a large impact on quality of life, finally one aspect of aging is an increasing loss of sensory and perceptual abilities and such a progressive disconnection from the environment. One central focus of my research is to identify the brain mechanism underlying communication and to study how and why communication abilities change during aging.

One most exciting finding in studying brain mechanisms was that brain function are not static but widely malleable through learning and training. Thus, one continuous theme of my research is to investigate the ability for neuroplastic reorganization of brain function. In early work we studied neuroplaticity with the model of life long training in professional musicians, we demonstrated learning effects in laboratory training and are applying the gained knowledge to rehabilitation regimen after brain injury resulting from stroke.

A primary goal in investigating the neural mechanism underlying human communication is to identify the brain structures, which are involved in a perceptual and cognitive function. However, more recently we are interested in learning how brain areas interact with each other. Interaction between brain regions requires connectivity through nerve fibers but also a mechanism for neural communication. My research focuses on neural communication through oscillatory brain activity. The theoretical concept is that brain networks can generate specific rhythms of activity, and two regions interact which each other through synchronization of such rhythms. The underlying concepts allow of fast dynamic reconfiguration of neural connectivity through changes in synchrony.

Magnetoencephalography (MEG) is my research method of choice because it allows noninvasively the recording of human brain activity during normal function. Most importantly, MEG measures brain activity with high temporal resolution and is specifically suitable to investigate fast changes in rhythm of brain activity during the first several hundred of milliseconds of central processing of sensation and perception. With MEG we are measuring outside of the head the magnetic field produced by current flow inside of activated neurons in the cortical surface. Even a strong brain activation during which thousands of neurons fire synchronously generates a magnetic field outside of the head which is at least nine orders of magnitude weaker than the earth magnetic field that aligns the compass needle. A fair amount of my research is dedicated to make such recording of brain activity possible and to improve the sensitivity of the method through sophisticated signal analysis approaches. Moreover, with MEG we are not only registering the effect of brain activation outside of the head, but we are estimating the actual changes in activity inside the brain tissue. Improving the mathematical tools for performing such neuromagnetic source analysis is another focus of my research.

Poster at the 2011 meeting of the Cognitive Neuroscience Society in San Francisco

1. Binaural processing in young and older adults

Aging related changes in the central nervous system result in functional deficits such as processing of temporal sound structures and processing of binaural information. Consequently, speech communication especially in noisy environment might be severely impaired in elderly persons even when their aided thresholds are normal. Behavioural tests often fail to distinguish between central auditory processing disorders and attention deficits. Therefore, objective tests for central auditory function are essential. We shall employ a new dichotic stimulus paradigm eliciting robust cortical responses specific for binaural processing of inter-aural time differences. With whole head magnetoencephalography we shall record responses to tone onsets and change in binaural timing as well 40-Hz steady-state responses simultaneously from two groups of 20 young and 20 older adults. Comparison with behavioural tests will give new insights in age related changes of central auditory processing and test the proposed method as a diagnostic tool.
The project is funded by the Hearing Foundation of Canada

• Human auditory 40-Hz steady-state responses
  

Auditory steady state-responses (ASSR) are oscillatory brain responses at the frequency of stimulation. The sources of MEG recorded are mainly in primary auditory cortex and may be a part of the thalamo-cortical network. We investigated the temporal dynamics of ASSR evoked with amplitude modulated sounds. A main working hypothesis is that the ASSR are related to temporal processing of auditory information.

• Right hemispheric laterality of 40-Hz ASSR
  

A common observation with whole head MEG recording of the ASSR was that the amplitudes in the right auditory cortex were larger than in the left. We compared laterality of auditory evoked responses (P1, N1, sustained response, transient gamma band response) with the laterality of the ASSR. Common to all auditory evoked responses is the effect of larger responses in the hemisphere contra-lateral to the stimulated ear, however, the sustained response and more pronounced the ASSR showed right hemispheric dominance. We discussed the observed effect as evidence for right hemispheric processing of the stimulus periodicity.

• Stimulus induced reset of 40-Hz ASSR
  

ASSR to amplitude modulated sound are strongly affected by a concurrent stimulus even if this distracting stimulus is presented to the contra-lateral ear and is spectrally distinct from the ASSR generating sound. The time-course of amplitude and phase of the induced change in the ASSR resembles that of the ASSR onset. Our hypothesis is that the onset like response after distraction indicates a reset of oscillatory activity. The results are discussed as an example for a reset mechanism in oscillatory networks.

• Does selective attention modulate the ASSR
  

Induced and evoked oscillatory activity in the gamma frequency-band (30-80 Hz) are discussed being related to binding of sensory information.Moreover, evidences exist that gamma-band activity is involved in attentional processes. That posed the question, whether the 40-Hz ASSR might be modulated by attention. We compared 40 Hz ASSR to amplitude modulated sound under attention to the auditory stimulus with those during attention focused to a visual task. Whereas significant ASSR enhancement 300-400 ms after stimulus onset in the attended condition was found, it seems that the 40-Hz ASSR is only little affected by changes in attention.

2. Oscillatory activity related to memory load in a working memory task

3. Brain responses to music: effects of long-term musical training

(Collaboration with Takako Fujioka, Rotman Research and Laurel Trainor, McMaster University, Hamilton)

4. Multi-sensory interaction in the auditory and visual system

Research Funding

2008-2011	Neural mechanisms of auditory-based remediation programs, Investigators: Claude Alain, Bernhard Ross, and Kelly Tremblay, Sponsors: Canadian Institutes for Health Research (CIHR), 85,000$ per annum for 3 years
2007-2010	Characterizing fMRI and MEG signals in the somatosensory cortex, Investigtors, Simon Graham, Wilkin Chau, Randy McIntosh, Bernhard Ross, Jon Ween, Sponsors: Canadian Institutes for Health Research (CIHR), 100,000$ per annum for 3 years
2007	Magnetoencephalography as a possible diagnostic tool for traumatic brain injury: Cortical oscillations during retrieval from working memory, Investigator:  Bernhard Ross, Sponsor: Dept. for Medicine University of Toronto, The Deans Fund, 10,000$ one year
2007	Auditory cortex activation indicating audiovisual integration during listening and reading, Investigators Bernhard Ross and Hao Luo, Sponsors: The Hearing Foundation of Canada, 24,500 $ for one year
2007-2012	Improved characterization of human somatosensory cortex using simultaneous vibro-tactile stimulation Investigators: Bernhard Ross; Sponsors: Natural Sciences and Engineering Research Council of Canada (NSERC),  26,000$ per annum vor five years
2006-2011	Aging related changes in central hearing - A neuromagnetic study Investigators: Bernhard Ross; Terence Picton, Claude Alain Sponsors: Canadian Institutes for Health Research (CIHR), 136,000$ per annum for five years
2006-2008	Transformation of whole head magnetoencephalographic data onto standardized sensor position Investigators: Bernhard Ross; Wilkin Chau Sponsors: Natural Sciences and Engineering Research Council of Canada (NSERC), 45,000$ per annum for three years
2005-2005	Binaural Processing in young and older adults Investigators: Bernhard Ross; Sponsors: The Hearing Foundation of Canada, 23,500 $ for one year