At the very top end of the primary sensory cortex, beyond the area for the toes, it has traditionally been believed that the sensory neural networks for the genitals occur. However, more recent research has suggested that there may be two different cortical areas for the genitals, possibly differentiated by one dealing with erogenous stimulation and the other dealing with non-erogenous stimulation. Discovery Dr. Wilder Penfield and his co-investigators Edwin Boldrey and Theodore Rasmussen are considered to be the originators of the sensory and motor homunculi. They were not the first scientists to attempt to objectify human brain function by means of a homunculus. However, they were the first to differentiate between sensory and motor function and to map the two across the brain separately, resulting in two different homunculi. In addition, their drawings and later drawings derived from theirs became perhaps the most famous conceptual maps in modern neuroscience because they compellingly illustrated the data at a single glance. Penfield first conceived of his homunculi as a thought experiment, and went so far as to envision an imaginary world in which the homunculi lived, which he referred to as "if". He and his colleagues went on to experiment with electrical stimulation of different brain areas of patients undergoing open brain surgery to control epilepsy, and were thus able to produce the topographical brain maps and their corresponding homunculi. More recent studies have improved this understanding of somatotopic arrangement using techniques such as functional magnetic resonance imaging (fMRI). Representation Penfield referred to his creations as "grotesque creatures" due to their strange-looking proportions. For example, the sensory nerves arriving from the hands terminate over large areas of the brain, resulting in the hands of the homunculus being correspondingly large. In contrast, the nerves emanating from the torso or arms cover a much smaller area, thus the torso and arms of the homunculus look comparatively small and weak. Penfield's homunculi are usually shown as 2-D diagrams. This is an oversimplification, as it cannot fully show the data set Penfield collected from his brain surgery patients. Rather than the sharp delineation between different body areas shown in the drawings, there is actually significant overlap between neighboring regions. The simplification suggests that lesions of the motor cortex will give rise to specific deficits in specific muscles. However, this is a misconception, as lesions produce deficits in groups of synergistic muscles. This finding suggests that