  Investigating neural activity from a global brain perspective in-vivo has
been in the domain of functional Magnetic Resonance Imaging (fMRI) over the
past few decades. The intricate neurovascular couplings that govern fMRI's
blood-oxygenation-level-dependent (BOLD) functional contrast are invaluable in
mapping active brain regions, but they also entail significant limitations,
such as non-specificity of the signal to active foci. Diffusion-weighted
functional MRI (dfMRI) with relatively high diffusion-weighting strives to
ameliorate this shortcoming as it offers functional contrasts more intimately
linked with the underlying activity. Insofar, apart from somewhat smaller
activation foci, dfMRI's contrasts have not been convincingly shown to offer
significant advantages over BOLD, and its contrasts relied on significant
modelling. Here, we study whether dfMRI could offer a better representation of
neural activity in the thalamocortical pathway compared to its (spin-echo (SE))
BOLD counterpart. Using high-end forepaw stimulation experiments in the rat at
9.4 T, and with significant sensitivity enhancements due to the use of
cryocoils, we show for the first time that dfMRI signals exhibit layer
specificity, and, additionally, display signals in areas devoid of SE-BOLD
responses. We find that dfMRI signals in the thalamocortical pathway cohere
with each other, namely, dfMRI signals in the ventral posterolateral (VPL)
thalamic nucleus cohere specifically with layers IV and V in the somatosensory
cortex. These activity patterns are much better correlated (compared with
SE-BOLD signals) with literature-based electrophysiological recordings in the
cortex as well as thalamus. All these findings suggest that dfMRI signals
better represent the underlying neural activity in the pathway. In turn, this
may entail significant implications towards a much more specific and accurate
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