Researchers at The University of Queensland have taken a significant step toward understanding brain damage that could eventually improve outcomes for stroke survivors.
An international team led by scientists at UQ has produced findings that clarify mechanisms behind unilateral spatial neglect, a disabling condition that often follows right-hemisphere brain injury after stroke. People with this condition tend to ignore or be unaware of the left side of space, which makes routine activities such as eating, dressing and navigating their surroundings extremely challenging.
ARC Discovery Early Career Research Fellow Dr Marta Garrido from UQ’s Queensland Brain Institute (QBI) explained that this lack of awareness on the left side may result from an imbalance in brain networks—specifically the way different regions interact and coordinate sensory processing.
“Patients with spatial neglect have difficulty attending to sensory information on one side of space, and the problem is typically much stronger for stimuli on the left,” Dr Garrido said. “Our work establishes how the healthy brain organizes auditory space, which is an essential step before we can pinpoint what goes wrong in the brains of people experiencing spatial neglect.”
QBI co-investigator and ARC Australian Laureate Fellow Professor Jason Mattingley noted that many brain functions are naturally asymmetrical. “Even in healthy people, perception is not always balanced between the left and right hemispheres,” he said. “For example, when viewing faces we often concentrate more on the left side. Studies like this one help us take a crucial step toward understanding the puzzling symptoms observed after brain injury.”
The research was a collaboration between QBI, UQ’s School of Psychology, Aarhus University in Denmark and University College London in the UK. Together, the team combined expertise in cognitive neuroscience, neuroimaging and computational modeling to test competing theories about how the brain represents auditory space.
In the study, the researchers recorded electrical brain activity from healthy adult volunteers using electroencephalography (EEG). Participants listened to sequences of sounds presented from the left, right or center while the team measured how different brain regions communicated with one another. This approach allowed the researchers to infer directional interactions—known as effective connectivity—between brain areas involved in spatial hearing and attention.
The results support a model in which the right hemisphere plays a dominant role in representing auditory space. Within a frontoparietal network, feedforward connections strengthened selectively in the hemisphere opposite to the side of stimulation, consistent with increased attentional weighting for incoming sensory signals. These findings align with the right-hemisphere dominance model of spatial perception and provide a mechanistic basis for why damage to the right side of the brain can produce severe left-sided neglect.
By clarifying the healthy brain’s network dynamics, this work gives researchers a framework for investigating the disrupted connectivity that underlies spatial neglect. The next phase of the project will examine how people with brain injury recruit left and right hemispheric networks when perceiving visual objects and sounds, with the aim of identifying specific disconnections that could become targets for rehabilitation.
Contact: Mikaeli Costello – University of Queensland
Source: University of Queensland press release
Image source: PublicDomainPictures (public domain)
Original research: Dietz M.J., Friston K.J., Mattingley J.B., Roepstorff A., Garrido M.I., “Effective Connectivity Reveals Right-Hemisphere Dominance in Audiospatial Perception: Implications for Models of Spatial Neglect,” Journal of Neuroscience. Published online April 2, 2014. doi:10.1523/JNEUROSCI.3765-13.2014
Effective Connectivity Reveals Right-Hemisphere Dominance in Audiospatial Perception: Implications for Models of Spatial Neglect
The study explores how the brain detects the location of salient sounds using differences in the signals received by each ear. Prior imaging work has suggested asymmetrical coding of auditory space, with a rightward attentional bias mirroring known asymmetries in vision. Two main models have been proposed to explain spatial neglect: the orientation bias model, which assumes a symmetric mapping between each hemisphere and the contralateral side of space, and the right-hemisphere dominance model, which posits that the right hemisphere represents both sides while the left represents only the right side. Using Dynamic Causal Modeling of EEG data collected during an auditory location oddball task, the authors found evidence for hemispheric asymmetry in a frontoparietal network consistent with right-hemisphere dominance. They report selective increases in forward connectivity in the hemisphere contralateral to sensory stimulation, interpreted as an attentional amplification of prediction error signals. These results support a disconnection account of unilateral neglect and inform theories of its cause.