Implicit learning of artificial grammatical structures after inferior frontal cortex lesions.

OBJECTIVE: Previous research associated the left inferior frontal cortex with implicit structure learning. The present study tested patients with lesions encompassing the left inferior frontal gyrus (LIFG; including Brodmann areas 44 and 45) to further investigate this cognitive function, notably by using non-verbal material, implicit investigation methods, and by enhancing potential remaining function via dynamic attending. Patients and healthy matched controls were exposed to an artificial pitch grammar in an implicit learning paradigm to circumvent the potential influence of impaired language processing. METHODS: Patients and healthy controls listened to pitch sequences generated within a finite-state grammar (exposure phase) and then performed a categorization task on new pitch sequences (test phase). Participants were not informed about the underlying grammar in either the exposure phase or the test phase. Furthermore, the pitch structures were presented in a highly regular temporal context as the beneficial impact of temporal regularity (e.g. meter) in learning and perception has been previously reported. Based on the Dynamic Attending Theory (DAT), we hypothesized that a temporally regular context helps developing temporal expectations that, in turn, facilitate event perception, and thus benefit artificial grammar learning. RESULTS: Electroencephalography results suggest preserved artificial grammar learning of pitch structures in patients and healthy controls. For both groups, analyses of event-related potentials revealed a larger early negativity (100-200 msec post-stimulus onset) in response to ungrammatical than grammatical pitch sequence events. CONCLUSIONS: These findings suggest that (i) the LIFG does not play an exclusive role in the implicit learning of artificial pitch grammars, and (ii) the use of non-verbal material and an implicit task reveals cognitive capacities that remain intact despite lesions to the LIFG. These results provide grounds for training and rehabilitation, that is, learning of non-verbal grammars that may impact the relearning of verbal grammars.

Recovery of injured Broca's portion of arcuate fasciculus in the dominant hemisphere in a patient with traumatic brain injury.

RATIONALE: Recovery of injured AF in patients with traumatic brain injury (TBI) has not been reported. In this study, we report on a patient with TBI who recovered from an injury to Broca's portion of AF in the dominant hemisphere, diagnosed by diffusion tensor tractography (DTT). PATIENT CONCERNS: A 28-year-old right-handed male patient suffered head trauma resulting from sliding while riding a motorcycle. DIAGNOSES: He was diagnosed with a traumatic contusional hemorrhage in the left frontal lobe, subarachnoid hemorrhage, and subdural hemorrhage in the left fronto-temporal lobe. INTERVENTIONS: He underwent craniectomy on the left fronto-temporal area, and hematoma removal for the subdural hemorrhage in the neurosurgery department of a university hospital. Two weeks after the injury, he was transferred to the rehabilitation department of another university hospital. He showed severe aphasia and brain MRI showed leukomalactic lesion in the left frontal lobe. OUTCOMES: The result WAB for the patient showed severe aphasia, with an aphasia quotient of 45.3 percentile. However, his aphasia improved rapidly by 9 months with an aphasia quotient at the 100.0 percentile. 2-week DTT detected discontinuity in the subcortical white matter at the branch to Broca's area of left AF. By contrast, on 9-month DTT, the discontinued portion of left AF was elongated to the left Broca's area. LESSONS: Recovery of injured Broca's portion of AF in the dominant hemisphere along with excellent improvement of aphasia was demonstrated in a patient with TBI. This study has important implications in brain rehabilitation because the mechanism of recovery from aphasia following TBI has not been elucidated.