Psychopathology of Frontal Lobe Syndromes - Patients with Frontal Lobe Lesions

Written by Michael H. Thimble, F.R.C.P., F.R.C. Psych

Patients with frontal lobe lesions also do badly on maze learning tasks, the Stroop test, and block design; they show perseveration of motor tasks and difficulty carrying out sequences of motor actions. Skilled movements are no longer performed smoothly, and previously automated actions such as writing or playing a musical instrument are often impaired. Performance on tests such as following a succession of hand positions (with the hand first placed flat, then on one side, and then as a fist, on a flat surface) or tapping a complex rhythm (for example two loud and three soft beats) is impaired. Following nondominant hemisphere lesions, singing is poor, as is recognition of melody and emotional tone, the patient being aprosodic. Perseveration (especially prominent with deeper lesions in which the modulating function of the premotor cortex on the motor structures of the basal ganglia is lost (9) may be tested by asking the patient to draw, for example, a circle or to copy a complex diagram with recurring shapes in it that alternate one with another. The patient may continue to draw circle after circle, not stopping after one revolution, or miss the pattern of recurring shapes (Fig. 2). Imitation and utilization behavior can also be tested for.

In many of these tests there is a clear discrepancy between the patient's knowing what to do and being able to verbalize the instructions, and his failure to undertake the motor tasks. In everyday life this can be extremely deceptive and lead the unwary observer to consider the patient to be either unhelpful and obstructive or (for example, in a medicolegal setting) to be a malingerer.

Some of these tasks, for example the word-fluency task, or inability to make melodic patterns, are more likely to be related to lateralized dysfunction, and the inhibition of motoric tasks relates to the dorsolateral syndrome.

NEUROANATOMIC BASIS OF FRONTAL LOBE SYNDROMES

Several authors have put forward explanations for frontal lobe syndromes. (6,9) The posterolateral areas of the frontal cortex are most closely linked to motor structures of the anterior part of the brain, thus leading to the motor inertias and the perseverations seen with lesions here. They are more pronounced after dominant hemisphere lesions, when the speech-related disorders become manifest. More posterior lesions appear to link with difficulties in organizing movement; anterior lesions result in difficulties in motor planning and a dissociation between behavior and language. Elementary motor perseverations probably require lesions that are deep enough to involve the basal ganglia. Disturbances of attention are related to the brainstem-thalamic-frontal system, and the basal (orbital) syndromes are due to disruption of frontal-limbic links. Loss of inhibitory function over the parietal lobes, with release of their activity, increases the subject's dependence on external visual and tactile information, leading to echo phenomena and the environmental dependency syndrome.

Teuber (31) suggested that the frontal lobes "anticipate" sensory stimuli that result from behavior, thus preparing the brain for events about to occur. The expected results are compared with actual experience, and thus smooth regulation of activity results. More recently, Fuster (5) has proposed that the prefrontal cortex plays a role in the temporal structuring of behavior, synthesizing cognitive and motor acts into purposeful sequences. Stuss and Benson (6) put forward a hierarchical concept for the regulation of behavior by the frontal lobes. They referred to fixed functional systems, including a number of recognized neural activities, such as memory, language, emotion, and attention. which are modulated by "posterior" areas of the brain in contrast to the frontal cortex. Two anterior counterparts are proposed, namely, the ability of the frontal cortex to sequence, change set, and integrate information, and to modulate drive, motivation, and will (the former are most strongly dependent on intact lateral, dorsal and orbital frontal convexity regions; the latter are related more to medial frontal structures). A further independent level is that of executive function of the human frontal lobes (anticipation, goal selection, preplanning, monitoring), which is superordinate to drive and sequencing, but may be subordinate to the role of the prefrontal cortex in self-awareness.

SUMMARY

In this review, some basic aspects of frontal lobe functioning have been discussed and methods of testing for frontal lobe abnormalities outlined. It has been emphasized that the frontal lobes are affected in a number of diseases, which cover a broad spectrum of neuropsychiatric problems. Furthermore, it is suggested that the frontal lobes are involved in syndromes not traditionally thought to be related to frontal lobe dysfunction, for example, schizophrenia, and rarer presentations such as misidentification syndromes, Frontal lobe dysfunction often goes unrecognized, especially in patients who have normal neurologic testing and apparently intact IQ when routine methods of investigation are employed. Although marked disturbances of behavior following frontal lobe dysfunction have now been described for well over 120 years, these large areas of the human brain, and their links with some of the highest attributes of mankind, have been relatively neglected and are worthy of much further exploration by those interested in neuropsychiatric problems.