Hemispheric asymmetries in face recognition in health and dysfunction.

A defining characteristic of the human brain is that, notwithstanding the clear anatomic similarities, the two cerebral hemispheres have several different functional superiorities. The focus of this chapter is on the hemispheric asymmetry associated with the function of face identity processing, a finely tuned and expert behavior for almost all humans that is acquired incidentally from birth and continues to be refined through early adulthood. The first section lays out the well-accepted doctrine that face perception is a product of the right hemisphere, a finding based on longstanding behavioral data from healthy adult human observers. Data are then presented from neuropsychologic studies conducted with individuals with prosopagnosia, which is either acquired after a lesion to the right hemisphere or is developmental in nature with no obvious lesion. The second section reviews data on the neural correlates of face perception, gathered using a host of imaging methodologies all the way from electroencephalography (EEG) through functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) studies to transcranial magnetic stimulation and intracranial depth recording. The penultimate section reviews empirical findings that track the emergence of the hemispheric asymmetry for faces, and offers a theoretical proposal that lays out possible origins of the adult asymmetry profile. Lastly, the hemispheric asymmetry associated with the perception of emotional face expression is considered. While considerable progress has been made in understanding the functional organization of the human cerebral cortex and its biases and asymmetries, much remains to be determined and the many inconsistencies remain to be reconciled in future research.