Diffusion spectrum imaging is a new technique at time of writing, which allows magnetic resonance brain imaging, at a much higher level of fidelity than fMRI permits.

To recap on fMRI's function, this only slightly more elderly process - by a mere few years - works based on detection of the dynamic regulation of blood flow in the brain. Known in medical terminology as the haemodynamic response, this method tracks brain function by following the demand for oxygen and glucose in blood vessels surrounding the neurons.

In a nutshell, it examines the haemoglobin of the blood in the brain.

Functional magnetic resonance imaging cannot tell what signal the neurons are sending, but what it can do is detect exactly which neurons are active, how active they are, and the duration of the activity.

Diffusion spectrum imaging, by contrast, uses the same magnetic resonance effect, and likewise concentrates on fluid, rather than neurons. However, DSI concentrates not on the blood, but on the water particles present in grey matter itself.

By mapping the gradient of water molecule diffusion through a cross section of the active region of the brain, it is possible for software to estimate the trajectories of neuron firing in that area.

It still cannot tell what you are thinking, but it can tell which groups of neurons just fired, and in which direction they sent a signal, in real-time.

Thus, it is possible, using diffusion spectrum imaging, to work out not only which areas are active, but a rough idea of which separate sub-areas in the area of the brain being studied, are communicating with each other. Further, which areas outside the area being studied, are being communicated with.

Its not precise down to the individual scale, but is a decisive step upwards from fMRI.

References

Brain Reading: fMRI

Mapping the Structural Core of Human Cerebral Cortex

Diffusion Spectrum Imaging Used to Map the Structural Core of Human Cerebral Cortex