Inflexibility of mental planning: a characteristic disorder with prefrontal lobe lesions?

Inflexibility of mental planning processes has repeatedly been discussed to represent a specific disorder resulting from human frontal lobe lesions. Patient groups suffering from acute or chronic unilateral frontal (medial, lateral) or retrorolandic (temporal, parietal) lesions and nonbrain-damaged controls were requested to mirror and to reverse mentally a maze structure that had been learned by the covered maze presentation technique (KARNATH et al., Neuropsychologia 29, 271-290, 1991). The patients with acute frontal lesions were impaired to adapt the acquired mental plan to the new (but related) problem and made more errors than those with acute temporal or parietal lesions and controls. However, no impaired plan modification was detected in patients with chronic frontal brain lesions. The difference of task performance in the acute and chronic (recovered) stage of frontal brain damage is discussed.