of the thalamus. single-cell recording, transcranial magnetic stimulation(tms), electrical stimulation of the cortex, and functional magnetic resonance imaging(fmri) are some of the techniques used to study maps in the brain. many of the existing topographic maps have been further studied or refined using fmri. for example, hubel and wiesel originally studied the retinotopic maps in the primary visual cortex using single-cell recording. recently, however, imaging of the retinotopic map in the cortex and in sub-cortical areas, such as the lateral geniculate nucleus, have been improved using the fmri technique.