The brians input and output are not so isolated as to be able to be distinguished by an EEG or other external Neurometric machines. Individual nevers for which input travel on alter the data being sent. For instance the the Visual Cortical Pathways process information along the way to the brain as well as in the brain.
It is possible to use internal mechanism to precisely measure the input of to neural response with more advanced methods detailed in this article:
The effort has already rewarded the team with a discovery. They found that in response to differently oriented motions of a bar pattern in the mouse's field of vision, an individual orientation neuron receives input signals from a number of differently oriented nerve cells in its network of connections but sends only one kind of output signal. "And this," Konnerth says, "is where things get really exciting." The orientation neuron only sends output signals when, for example, the bar pattern moves from bottom to top. Evidently the neuron weighs the various input signals against each other and thus reduces the glut of incoming data to the most essential information needed for clear perception of motion.
In the future, Konnerth would like to extend this research approach to observation of the learning process in an individual neuron. Neuroscientists speculate that a neuron might be caught in the act of learning a new orientation. Many nerve endings practically never send signals to the dendritic tree of an orientation neuron. Presented with visual input signals that represent an unfamiliar kind of movement, formerly silent nerve endings may become active. This might alter the way the neuron weighs and processes inputs, in such a way that it would change its preferred orientation; and the mouse might learn to discern certain movements better or more rapidly. "Because our method enables us to observe, down to the level of a single synapse, how an individual neuron in the living brain is networked with others and how it behaves, we should be able to make a fundamental contribution to understanding the learning process," Konnerth asserts. "Furthermore, because here at TUM we work closely with physicists and engineers, we have the best possible prospects for improving the spatial and temporal resolution of the images."
-New method reveals how individual nerve cells process visual input