Phenotypic Change of Utilization Behavior Due to Reduction of Instinctive Grasp Reaction in a Case with a Right Medial Prefrontal Infarction : Factors Related to the Expression of Utilization Behavior and Its Phenotype

Abstract

  We report a case of utilization behavior (UB) after a right medial prefrontal infarction. During the period when ʻinducedʼ UB was observed, instinctive grasping reactions (IGR) including visual groping with both hands, and attention deficits were present. After the disappearance of IGR in the right hand, the phenotype of UB changed into the ʻinducedʼ form where the patient picked up tools presented in the left space with the left hand, and then switched to the right hand for usage. We considered that there was no direct continuity from IGR to UB, because UB in this phase was observed as using tools with the right hand without IGR. UB without IGR in the right hand is critically different from compulsive use of tool. The incidence of UB decreased as IGR diminished and attention deficits improved, suggesting that attention deficits might contribute to the manifestation of UB. MRI in the present case demonstrated a lesion in the right medial frontal lobe extending into the anterior corpus callosum. The presence of right IGR in the early phase suggests dysfunction also in the left medial frontal lobe due to diaschisis. Functional recovery of the left frontal lobe might be associated phenotypic change of UB during the clinical course of the patient.