New technology may help shed light on brain stimulation
Brain stimulation, such as deep brain stimulation (DBS), is a powerful way to treat neurological and psychiatric disorders. Although it has provided therapeutic benefits to people suffering from Parkinson’s, Alzheimer’s and drug addiction for more than a decade, its underlying neural mechanism is still not fully understood.
Queensland Brain Institute (QBI) researchers are now on the verge of unraveling the mystery of brain activity to better understand this mechanism and potentially predict DBS outcomes.
The brain is a very complex network of hierarchically organized circuits with extensive connections. The connections go in different directions, forwards and backwards, and between neurons that are either excitatory – the accelerators of a response – or inhibitory – the brakes modifying a response.
“Let’s say you want to move your hand – once that signal is on, we expect the activity that follows to depend on the neural networks in the brain,” said Associate Professor Kai-Hsiang Chuang.
“What we don’t fully understand is how or when these structural and functional components of the brain interact to eventually lead to the outcome of hand movement. »
Functional MRI (fMRI) is the most widely used technique for studying brain networks. fMRI tracks changes in blood flow and oxygenation as a result of neural activity, thus indirectly measuring the functional connections being formed and giving us an indication of where brain activity is spreading.
Brain activity, however, is not as simple as a signal traveling from area to area.
The Chuang lab team developed a new ultrafast fMRI technique with dramatically increased temporal resolution, allowing them to capture the dynamics of brain activity at sub-second levels.
Associate Professor Chuang said the new technique has led to a better understanding of how and when structural and functional connections in the brain interact.
“The first new discovery we made is that brain activity not only propagates through structural wiring, but follows certain preferential circuits based on their excitatory and inhibitory neural distribution,” he said.
“Communication between brain regions of similar cell types becomes more fluid and brain activity stronger. »
The Chuang group tracked the brain activity of both stimulated and resting mice using their ultrafast fMRI technique. When the brain was stimulated, activity followed the structural wiring in the forward direction – from A to B then from B to C. When the brain was at rest, activity was more dependent on cell type organization and less structural wiring, propagating between C and B but not with A, if that is where the preferential circuit was.
This means that how information is processed actually depends on your state, whereas it was previously thought that brain activity works the same whether you are at rest or busy performing a task.
“The second finding we made is that the blood signal detected by fMRI could reflect the network organization and distribution of cell types,” said Associate Professor Chuang.
“These findings have important implications for how brain structure works and how to predict activity based on knowledge of this structure. More concretely, what we know now will impact the design of DBS and other brain stimulation techniques.
“The next steps are to work with clinicians versed in brain stimulation to determine how we can use this knowledge combined with human data to help improve our understanding of DBS. »
This more complete understanding could allow us to better predict DBS outcomes and potentially improve its design for better therapeutic outcomes.
This study was first published in the Proceedings of the National Academy of Sciences (PNAS).
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