Figure Caption: Major functional anatomical regions of the frontal lobes.

The frontal lobes represent a large area of the brain and brain centers within the frontal lobe have numerous interconnections with other parts of the brain. These include connections with emotion and mood centers as well as cognitive centers. This high degree of complexity results in a number of syndromes that are associated with lesions of this area. There are three general anatomical divisions of the frontal cortex: the limbic, the precentral and the prefrontal cortices.

The precentral cortex consists of areas that lie immediately before the central sulcus. These consist of the primary and secondary motor control areas. The limbic component consists of the inferior and medial parts of the cingulate gyrus and the posterior parts of the orbital frontal areas. These areas have interconnections with the amygdala, hippocampus, thalamus and other parts of the limbic system. The prefrontal cortex is anterior to the motor control areas and comprises the greater part of the frontal lobe. It is subdivided into the dorsolateral, mesial and orbital areas. These sections are histologically distinct and probably represent functional differences. The prefrontal cortex is the area implicated in the studies of personality and the behavioral effects of frontal lobe lesions. It has extensive interconnections with virtually every other part of the cerebrum. These include association areas in the temporal, occipital and parietal lobes, the limbic system, the dorsal medial nucleus of the thalamus and the basal ganglia.

Bilateral lesion of the inferior medial sections of the frontal lobes causes emotional and behavioral changes. Intellectual impairment results from lesion of the dorsolateral portion of the frontal lobes.

TOP of Page

Cognitive Impairment

Although patients with frontal lobe lesions may have extensive brain injury and numerous behavioral changes they will typically score within the normal range on IQ tests. The cognitive impairment associated with frontal lobe lesions involve cognitive abilities that are not measured by conventional IQ tests. These include impairment of hypothesis-testing and abstract reasoning, memory disorder, attention deficits and difficulty in initiation of cognitive activity.

Impairment of Abstract Reasoning, Hypothesis testing and modulation of cognition

The overriding function of the frontal areas is to modulate and control motor function, emotion, attention and other cognitive activity. Virtually all aspects of frontal lobe impairment can be considered a specific aspect of a general deficit of control. In the domain of reasoning, a deficit of modulation is manifested as poor abstract reasoning and failure to maintain goal-directed behavior.

Abstract reasoning involves making complex associations between semantic elements and identifying super-ordinate categories, reasoning by general rules and formulating hypotheses. If abstract reasoning is not present then the patient has difficulty formulating the super-ordinate category that subsumes individual semantic elements. For example, the patient may not be able to reason that cars, trains, airplanes and the like, are members of the category of modes of transportation.

Another manifestation of abstract reasoning involves the development of rules that guide future behavior. The reasoning person identifies common features and themes in the experiences of everyday life and formulates general rules that govern behavior in these situations. Rules may also be taught by others but reasoning people usually verify and endorse the validity of rules before using them. People who have sustained injury to the frontal lobes have difficulty formulating these rules. Indeed, even if a rule is given to the patient there is still great difficulty in using it to guide behavior. As a result of this general inability to formulate and use rules, the patient cannot conceptualize goal states and use the goals as objectives to guide thought and actions. Actions are motivated by very concrete, superficial goals, such as immediate gratification of simple impulses.

Hypothesis formulation and testing also involves the generalization of experiences in the form of rules or general principles. This cognitive function is likewise affected by lesions of the frontal lobes.

TOP of Page

Disturbance of Behavior and Personality

Patients with lesions of the ventromedial portion of the frontal lobes have a behavioral syndrome characterized by lack of originality and creativity, impairment of attention, and a tendency to display inappropriate emotions and behavior. They have difficulty initiating behavior; when they do engage in activity, they may continue the activity without stopping. They may only start activity when prompted by others.

Although controversial, emotional disturbance most often results from lesion of the orbital frontal areas. These areas have interconnections with the amygdala and hypothalamus. Emotional disturbances include laughing or crying in situations inappropriate to the emotion. The emotional response also appears superficial and variable. The patient usually has no awareness that their emotional response is incorrect or extreme.

TOP of Page

Language Impairment

Broca's area resides in the left frontal lobe and lesion of this area produces a well-known impairment of language referred to as Broca's aphasia. This disorder is covered under the aphasia chapter. Check the "contents" menu above.

Patients with dorsolateral frontal lobe lesions may also have additional language impairment that is distinct from Broca's aphasia. The first of these is a general reduction of language production although language utterances that are produced are fluent and maintain correct syntax. Patients with frontal lobe lesions have difficulty initiating speech and maintaining a complex, spontaneous conversation. This is referred to as a deficit in "verbal fluency", although language productions are actually fluent. A better way to describe this phenomenon might be low verbal production.

Patients with frontal lesions in secondary motor control areas may also display mutism. In particular, lesions of the cingulum often result in essential mutism. Here, the patient comprehends language but cannot produce any vocalizations, including language. This is viewed as a deficit of the basic motor control of the oral apparatus to the point where there is no initiation of activity. The patient is often indifferent to communication in general and does not show the frustration characteristic of Broca's aphasia. In severe cases of mutism the patient is referred to as being "locked in", meaning that they are able to comprehend information but cannot respond to it.

A pure agraphia is also associated with lesions of supplemental motor areas of the left dorsolateral frontal lobe (Exner's area). Exner's area is above Broca's area and anterior to the primary motor control area. In this disorder, the patient is not aphasic but has difficulty writing and reading.

TOP of Page

Impairment of Motor Function

The highly controlled, volitional components of motor control are located in the frontal lobes on the dorsolateral surface anterior to and including the primary motor control area (the motor strip). Other components of the motor control system are the Basal Ganglia and the Cerebellum. The cortical system in the frontal lobes are involved in the complex control of skeletal muscles in the execution of actions.

Lesions of the dorsolateral frontal areas results in a number of motor impairments. These include perseveration, incoordination, motor impersistence and hypokinesia. Patients with left frontal lobe lesions may also have ideomotor apraxia (See the Apraxia section). Lesions within hemisphere cause worse motor impairment of the opposite extremities. These deficits again involve the general modulation and control functions that are characteristic of the frontal lobes. There is some evidence that control is lateralized to each frontal area. The left hemisphere is dominant for motor control and the modulation of language. The right hemisphere is more involved in the modulation of actions that are executed in a spatial context, such as three-dimensional block construction.

TOP of Page

Impairment of Reflexes

The frontal lobes play the primary role in the inhibition of fundamental reflexes that were presumably inherited as part of primitive brain structures characteristic of the primate brain. These reflexes include the grasp reflex and the snout and sucking reflexes. The grasp reflex is elicited by stroking the skin of the palm. The patient grasps the object and has difficulty releasing the grasp even when told to attend to the hand and release the grasp. Snout and sucking reflexes are elicited by stimulating the lips and space between the upper lip and the nose. Here, the patient extends the lips outward for the snout reflex. The patient is compelled to suck on an object placed in the lips when the suck reflex is present The frontal lobes usually inhibit these reflexes during childhood and adulthood. When the frontal lobe is lesioned, this inhibition is removed and the reflexes return.

TOP of Page

Impairment of Social Behavior

Since frontal lobe lesions result in a pervasive defect in planning and modulation of behavior, these patients have compelling deficits in maintining appropriate social responses. Social perception and action are very complex. In addition, people do not have a wide tolerance for social behavior; even minor deviations in social behavior are noticeable. Patients with frontal lobe lesions have great difficulty generating appropriate behavioral options in social situations and then choosing the best alternative. They also base their behavior on concrete simple motivations and cannot formulate or comprehend more complex or abstract reasons for acting. Much social behavior requires a complex and abstract appreciation of the social setting.

TOP of Page

Confabulation and Reduplication Syndrome

Patients with severe frontal lobe lesions tend to fabricate quick, impulsive answers to questions. Some responses may be quite fanciful and imaginative. The patient cannot inhibit a response in order to check its validity. For example, when asked, "How did you get to the hospital?", the patient may respond with an imaginative tale that has very little relationship to the truth. This tendency to fabricate an answer is called confabulation. It is most common among patients with basal forebrain lesions and among patients with additional impairment of memory ability.

Another syndrome that is similar to confabulation is reduplication. Here, the patient with a frontal lobe lesion confabulates that the current environment, usually the hospital, is actually another place that is similar to the current setting but has a different name and location. The patient may even claim that the current hospital is a university dormitory or an apartment building. The confabulated place is always somewhere else and it is usually familiar to the patient, such as the hospital in the patient's home town. The patient will often maintain this confabulation even when confronted with salient, contradictory information.

TOP of Page

Assessment

The important constructs to assess among executive functions are: attention and freedom from distractibility; initiation, task persistence and maintainance of set; and mental flexibility and abstract reasoning.

Attention and Freedom from Distractibility
Patients with frontal lobe lesions can have difficulty in maintaining attention for extended periods of time when there are distractions present. Letter vigilance tasks in which the patient is asked to listen to a long string of letters and respond every time an "a" is read are good for detecting distractibility. The stroop test also provides an evaluation of sustained and selective attention. Here the patient must selectively attend to one stimulus while inhibiting a more salient one.

Initiation and Maintenance of Set
Initiation can be observed in behavior as a latency to respond, or an inability to respond without prompting. Maintainence of set refers to the ability to continue with an activity in the face of competing stimuli. Go/nogo tasks are one way of assessing maintainence of set. Here the patient is asked to first mirror a simple tapping task (If I knock once, you knock once, if I know twice you knock twice). Then, the task demands switch so that the patient is asked to inhibit the salient response and give the opposite response ("If I knock twice, you knock once and if I knock once you knock twice"). Word fluency tasks can also measure initiation and set maintainence. Thepatient is asked to name as many words as they can think of begining with specified letters of the alphabet (ie., F, A, S). Patients who lose set will not be able to stay on the letter.

Mental Flexibility and Abstract Reasoning
Mental flexibility can be assessed by having the patient sort objects or categories. The Wisconsin Card Sorting Test and the Category Test are good measures of mental flexibility and abstract problem solving. The WCST requires the patient to sort cards according to a category which only the examiner knows. It is up to the patient to figure out the rule. Once a criterion of responses are met, the category is changed and the patient must again figure out the rule. Measures of perseverative tendency, failure to maintain set, and categories achieved help to determine problem solving ability. The Category Test measures abstraction and concept formation ability by requiring the patient to figure the concept which must be applied within each of seven subtests in order to get the correct answer. The patient must demonstrate the ability to generate possible concepts and benefit from feedback.