Authors:

Hornberger, M. & HENSON, R.

Reference:

Year of publication:

2007

CBU number:

6508

Abstract:

Recent fMRI studies investigating the neural correlates of retrieval content (e.g, Wheeler et al. 2003) and retrieval orientation (e.g, Hornberger et al. 2006) show convergent evidence that similar brain areas are involved in retrieving and orienting towards different memoranda (e.g, visual vs auditory stimuli). In the current study, we contrasted directly retrieval content vs. retrieval orientation in a single recognition memory paradigm.During the Study phases, participants made semantic judgments on intermixed pictures and auditory words. During the two types of Test phase, participants saw visual words and were asked either 1) whether the words had been studied as pictures ("targets"), in the Picture retrieval condition, or 2) whether the words had been studied as auditory words ("targets"), in the Auditory retrieval condition. Items not previously presented (unstudied), or presented in the not-to-be-retrieved modality ("non-targets"), were to be rejected as new (i.e, participants performed two types of "Exclusion" task).Retrieval content effects were only found in higher visual cortex (fusiform gyrus), with greater activation for test words studied as pictures than test words studied auditorily. Unlike Wheeler et al, we failed to find retrieval content effects in higher auditory cortex).Retrieval orientation effects (i.e. contrasts of correctly rejected unstudied items in the Auditory vs. Picture retrieval conditions) were found in both visual and auditory cortex. However, the activation differences were the opposite to what was expected, with greater activation in (early and late) visual cortex when oriented towards auditory words, and greater activation in auditory cortex when oriented towards pictures. Thus our results replicate the previous retrieval content findings by Wheeler et al. (2003) for the Picture, though not the Auditory condition. However, the results for retrieval orientation show a pattern that differs from our earlier findings (Hornberger et al. 2006). This may reflect differences at study (blocking vs intermixing the two types of memoranda) or differences at test (i.e. "yes/no" recognition vs. the present Exclusion task; though see Woodruff et al, 2006). Nevertheless, the retrieval content and retrieval orientation effects still appear related, in that both types of processing elicit activations in higher perceptual areas. The question remains as to whether these common loci reflect similar or different types of processing. In particular, future studies should investigate whether retrieval content and retrieval orientation effects both reflect mental imagery, either reinstated automatically by the test cue, or instigated by the participant in order to search memory.References:Hornberger M, Rugg MD, Henson RN; fMRI correlates of retrieval orientation; Neuropsychologia 2006;44(8):1425-36.Wheeler ME, Buckner RL; Functional dissociation among components of remembering: control, perceived oldness, and content; J Neurosci. 2003;23(9):3869-80.Woodruff CC, Uncapher MR, Rugg MD; Neural correlates of differential retrieval orientation: Sustained and item-related components; Neuropsychologia 2006;44(14):3000-10.