Upper motoneuron lesions to the face often cause paralysis. The lesions cause weakness in various areas of the face while not affecting other areas of the face. This pattern of weakness due to the input of the motor neurons of the lower facial muscles is often maintained contralateral. The strength of the muscles in the upper region of the face are preserved better than the muscles in the lower face. It was found that in many anatomical studies that cortical input from both hemispheres could reach motoneurons that supply muscles of all aspects of the face. Through the combination of anterograde and retrograde tracing techniques in monkeys it was found that the facial nucleus, which supplies muscles of the lower face are innervated bilaterally. Using TMS has shown the activation of both hemispheres during facial expression and emotion. However, there have been some discrepancies with the use of this method including differences in observations when using single and multiple needles as well as the areas of where the needles are placed. Using electrical cortical mapping bilateral movements were observed in the lower facial muscles compared to unilateral movements. From anatomic studies on patients with unilateral infarction, motoneurons in the lower facial area were innervated bilaterally; however, there was predominance in contralateral areas of the lower face.