Frontal lobe lesions in adults can cause the reemergence of certain primitive reflexes that are normally present in infants. These so-called frontal release signs include the grasp, snout, root, and suck reflexes. Of these reflexes, the grasp reflex is the most useful in evaluating frontal lobe dysfunction.
Patients with frontal lobe dysfunction may have particular difficulty in changing from one action to the next when asked to perform a repeated sequence of actions. For example, when asked to continue drawing a silhouette pattern of alternating triangles and squares (written alternating sequencing task), they may get stuck on one shape and keep drawing triangles. This phenomenon is called perseveration. The Luria manual sequencing task, in which the patient is asked to tap the table with a fist, open palm, and side of open hand and then to repeat the sequence as quickly as possible, is also a useful test for perseveration.
Another common finding is motor impersistence, a form of distractibility in which patients only briefly sustain a motor action in response to a command such as "Raise your arms" or "Look to the right." Ability to suppress inappropriate behaviors can be tested by the auditory Go-No-Go test, in which the patient moves a finger in response to one sound, but must keep it still in response to two sounds.
Patients with frontal lobe lesions may also exhibit very slow responses termed abulia or may have changes in personality and judgment based on sequential exams or reported by family members.
The constellation of abnormalities described here helps localize lesions to the frontal lobes (see Neuroanatomy Through Clinical Cases, Chapter 19).