Authors:

OWEN, A.M.

Reference:

Year of publication:

2003

CBU number:

5837

Abstract:

Habib, Nyberg and Tulving (2003) have recently updated their views on the hemispheric encoding/retrieval asymmetry (HERA) model, almost a decade after the idea was first introduced into the memory literature [2]. Broadly speaking, the central tenet of HERA is unchanged; that is, that the left and right prefrontal cortices are disproportionately involved in the encoding and retrieval of episodic memories, respectively. While the HERA model has undoubtedly promoted fruitful scientific exchange through the provision of a concrete testable hypothesis, it still leaves many questions about the nature of functional asymmetry in humans unanswered. In particular, the model is based solely on functional neuroimaging data and, to a significant extent, it remains unsupported by data from other methodologies. For example, according to HERA, patients with unilateral frontal-lobe lesions should be differentially impaired at encoding or retrieval depending on the side of their lesion. To date, there is no evidence to suggest that this is the case. The data from repetitive transcranial magnetic stimulation (rTMS) studies in healthy volunteers is also equivocal with respect to HERA. However, as Habib and colleagues (2003) clearly show, the most significant challenges have come from within the functional neuroimaging literature itself. Indeed, in the most comprehensive review of relevant imaging studies to date, Fletcher and Henson [11] concluded that "The HERA generalization may not be sufficient, however, in that our review included many studies of verbal retrieval that activate both left and right frontal cortex, or even left frontal cortex alone". In this article, this evidence is briefly reviewed.