Gary Marcus believes that neurology is still in its infancy:
The smallest element of a brain image that an fMRI can pick out is something called a voxel. But voxels are much larger than neurons, and, in the long run, the best way to understand the brain is probably not by asking which particular voxels are most active in a given process. It will instead come from asking how the many neurons work together within those voxels. And for that, fMRI may turn not out not to be the best technique, despite its current convenience. It may ultimately serve instead as the magnifying glass that leads us to the microscope we really need.
If most of the action in the brain lies at the level of neurons rather than voxels or brain regions (which themselves often contain hundreds or thousands of voxels), we may need new methods, like optogenetics or automated, robotically guided tools for studying individual neurons; my own best guess is that we will need many more insights from animal brains before we can fully grasp what happens in human brains. Scientists are also still struggling to construct theories about how arrays of individual neurons relate complex behaviors, even in principle. Neuroscience has yet find its Newton, let alone its Einstein.