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Abstract

While much evidence has linked injury to the prefrontal cortex (PFC) to impairments in planning, much less is known about the underlying cognitive processes that
are compromised as a consequence of PFC damage. In addition, the differential contributions of left and right PFC to planning remain controversial. To address these issues, we administered a real-world travel planning task to thirty participants comprised of six patients with focal frontal lesions to left PFC, six patients with focal frontal lesions to right PFC, six patients with posterior lesions, and twelve normal controls. Furthermore, we employed the methodology of verbal protocol analysis, enabling us to go beyond simple task performance and to analyze the underlying cognitive processes and strategies that underlie plan formulation. The results revealed that patients with right PFC lesions formulated significantly worse plans than patients with left PFC lesions and normal controls. No other comparison reached significance. To explore the underlying reasons for the planning impairment exhibited by right PFC patients, we computed the ratio of concrete to abstract problem-solving statements between the groups. The results demonstrated
that right PFC patients had a significantly higher concrete-to-abstract ratio of problem-solving statements than left PFC patients and normal controls. No other comparison reached significance. We conclude
that the role of right PFC in real-world planning involves the formulation and maintenance of abstract ideas as a function of task demands.