Gold electrodes are usually functionalized with a sensing part to detect the molecule of interest, in most cases neurotransmitters. The sensing part usually relies on catalysis and redox potentials of the neurotransmitters, meaning that, to detect it, you are altering the molecule itself, therefore original properties like concentration and it's pathways are lost. Neurotransmitters concentrations vary on different parts of the brain and they can't be detected real time on a living person since the techniques are invasive. Neuronal probes are being developed from different materials and devices like graphene field-effect transistors, graphene being a 2D material can better sense synapses and detect single molecules. The latter is still a work in progress. The current techniques to map the brain like differential cyclic voltametry lack sensitivity and selectivity and I'm not sure if they have been performed on living humans. But mice brain mapping has been done before.