Speech

• For decades, scientists have believed that we need to map this intricate connectivity in detail to understand how the structured patterns of activity defining our thoughts, feelings and behaviour emerge.
• The conventional view is that specific thoughts or sensations elicit activity in specific parts of the brain.

Function follows form

• We uncovered this close relationship between shape and function by examining the natural patterns of excitation that can be supported by the anatomy of the brain.
• In these patterns, called “eigenmodes”, different parts of the brain are all excited at the same frequency.
• In a similar way, the brain has its own preferred patterns of excitation, which are determined by its anatomical and physical properties.

A tale of two brains

• This perspective views the brain as a collection of discrete regions, each specialised for a specific function, such as vision or speech.
• An alternative view, embodied by an approach to modelling brain activity called neural field theory, eschews this division of the brain into discrete areas.

Comparing the two views

• To compare the two views of the brain, we tested how easily the conventional, discrete view and the continuous, wave-based view can explain more than 10,000 different maps of brain activity.
• We found that eigenmodes of brain shape – not connectivity – offer the most accurate account of these different activation patterns.

Brain waves and icebergs

• The model only uses the shape of the brain to constrain how the waves evolve through time and space.
• We also found that most of the 10,000 different brain maps that we studied were associated with activity patterns spanning nearly the entire brain.
• Rather than focusing solely on how signals pass between discrete regions, we should also investigate how waves of excitation travel through the brain.

A new approach to brain mapping

• Instead, typical brain mapping methods rely on complex statistics to quantify brain activity without any reference to the underlying physical and anatomical basis of those patterns.
• Our discovery also offers immediate practical benefits, since eigenmodes of brain shape are much simpler to quantify than those of brain connectivity.
• This new approach opens possibilities for studying how brain shape affects function through evolution, development and ageing, and in brain disease.