Hippocampal sclerosis affects fMR-adaptation of lyrics and melodies in songs

Songs constitute a natural combination of lyrics and melodies, but it is unclear whether and how these two song components are integrated during the emergence of a memory trace. Network theories of memory suggest a prominent role of the hippocampus, together with unimodal sensory areas, in the build-up of conjunctive representations. The present study tested the modulatory influence of the hippocampus on neural adaptation to songs in lateral temporal areas. Patients with unilateral hippocampal sclerosis and healthy matched controls were presented with blocks of short songs in which lyrics and/or melodies were varied or repeated in a crossed factorial design. Neural adaptation effects were taken as correlates of incidental emergent memory traces. We hypothesized that hippocampal lesions, particularly in the left hemisphere, would weaken adaptation effects, especially the integration of lyrics and melodies. Results revealed that lateral temporal lobe regions showed weaker adaptation to repeated lyrics as well as a reduced interaction of the adaptation effects for lyrics and melodies in patients with left hippocampal sclerosis. This suggests a deficient build-up of a sensory memory trace for lyrics and a reduced integration of lyrics with melodies, compared to healthy controls. Patients with right hippocampal sclerosis showed a similar profile of results although the effects did not reach significance in this population. We highlight the finding that the integrated representation of lyrics and melodies typically shown in healthy participants is likely tied to the integrity of the left medial temporal lobe. This novel finding provides the first neuroimaging evidence for the role of the hippocampus during repetitive exposure to lyrics and melodies and their integration into a song

A habituation account of change detection in same/different judgments

We investigated the basis of change detection in a short-term priming task. In two experiments, participants were asked to indicate whether or not a target word was the same as a previously presented cue. Data from an experiment measuring magnetoencephalography failed to find different patterns for “same” and “different” responses, consistent with the claim that both arise from a common neural source, with response magnitude defining the difference between immediate novelty versus familiarity. In a behavioral experiment, we tested and confirmed the predictions of a habituation account of these judgments by comparing conditions in which the target, the cue, or neither was primed by its presentation in the previous trial. As predicted, cue-primed trials had faster response times, and target-primed trials had slower response times relative to the neither-primed baseline. These results were obtained irrespective of response repetition and stimulus–response contingencies. The behavioral and brain activity data support the view that detection of change drives performance in these tasks and that the underlying mechanism is neuronal habituation

The Role of Medial Temporal Lobe Regions in Incidental and Intentional Retrieval of Item and Relational Information in Aging: Medial Temporal Lobes in Aging and Memory

Considerable neuropsychological and neuroimaging work indicates that the medial temporal lobes are critical for both item and relational memory retrieval. However, there remain outstanding issues in the literature, namely the extent to which medial temporal lobe regions are differentially recruited during incidental and intentional retrieval of item and relational information, and the extent to which aging may affect these neural substrates. The current fMRI study sought to address these questions; participants incidentally encoded word pairs embedded in sentences and incidental item and relational retrieval were assessed through speeded reading of intact, rearranged, and new word-pair sentences, while intentional item and relational retrieval were assessed through old/new associative recognition of a separate set of intact, rearranged, and new word pairs. Results indicated that, in both younger and older adults, anterior hippocampus and perirhinal cortex indexed incidental and intentional item retrieval in the same manner. In contrast, posterior hippocampus supported incidental and intentional relational retrieval in both age groups and an adjacent cluster in posterior hippocampus was recruited during both forms of relational retrieval for older, but not younger, adults. Our findings suggest that while medial temporal lobe regions do not differentiate between incidental and intentional forms of retrieval, there are distinct roles for anterior and posterior medial temporal lobe regions during retrieval of item and relational information, respectively, and further indicate that posterior regions may, under certain conditions, be over-recruited in healthy aging

The temporal context of face perception: behavioural, electrophysiological and neuroimaging correlates

Adaptation-related aftereffects (AEs) and repetition priming (PR) are two phenomena when recent experiences alter face perception. Although the behavioural reflections of AEs and PR are quite different, both phenomena share some similarities regarding their functional properties and neural correlates. As most of the previous studies focused on either one or the other phenomenon, little is known about the relationship between AEs and PR. The present studies attempted to fill this gap. Study I investigated face identity AEs and PR within the same stimulus repetition paradigm, keeping timing and task constant. Following face or Fourier phase randomized (noise) stimuli, participants classified test faces varying on a morph continuum between two famous identities. Study I showed that AEs and PR can be observed within the same paradigm and subjects, behaviourally and in event-related potentials (ERPs). Interestingly, we found identity-specific as well as category-specific ERP modulations. Study II further investigated the factors underlying face identity AEs in a similar paradigm. The results confirmed and extended the findings of Study I, e.g., there were again different ERP modulations by stimulus category and face identity. In Study III, AEs and image-specific PR were investigated in the perception of face gender using functional magnetic resonance imaging (fMRI). Study III suggested dissociations between 1) gender-specific AEs and image-specific PR in behaviour, 2) brain areas associated with AEs and PR, and 3) brain areas associated with gender-specific and categorical processes. In conclusion, the present studies showed that similarity between adaptor and test faces and ambiguity of the test face both determine whether AE or PR is observed, and suggested that exclusive mechanisms might underlie both phenomena. Our results also revealed that the processing of face identity or gender runs in parallel to object-category processing during the earlier processing stages

Representation of faces in perirhinal cortex

The prevailing view of medial temporal lobe (MTL) functioning holds that its structures are dedicated to long-term declarative memory. Recent evidence challenges this view, suggesting that perirhinal cortex (PrC), which interfaces the MTL with the ventral visual pathway, supports highly integrated object representations that contribute to both recognition memory and perceptual discrimination. Here, I used functional magnetic resonance imaging to examine PrC activity, as well as its broader functional connectivity, during perceptual and mnemonic tasks involving faces, a stimulus class proposed to rely on integrated representations for discrimination. In Chapter 2, I revealed that PrC involvement was related to task demands that emphasized face individuation. Discrimination under these conditions is proposed to benefit from the uniqueness afforded by highly-integrated stimulus representations. Multivariate partial least squares analyses revealed that PrC, the fusiform face area (FFA), and the amygdala were part of a pattern of regions exhibiting preferential activity for tasks emphasizing stimulus individuation. In Chapter 3, I provided evidence of resting-state connectivity between face-selective aspects of PrC, the FFA, and amygdala. These findings point to a privileged functional relationship between these regions, consistent with task-related co- recruitment revealed in Chapter 2. In addition, the strength of resting-state connectivity was related to behavioral performance on a face discrimination task. These results suggest a mechanism by which PrC may participate in the representation of faces. In Chapter 4, I examined PrC connectivity during task contexts. I provided evidence that distinctions between tasks emphasizing recognition memory and perceptual discrimination demands are better reflected in the connectivity of PrC with other regions in the brain, rather than in the presence or absence of PrC activity. Further, this functional connectivity was related to behavioral performance for the memory task. Together, these findings indicate that mnemonic demands are not the sole arbiter of PrC involvement, counter to the prevailing view of MTL functioning. Instead, they highlight the importance of connectivity-based approaches in elucidating the contributions of PrC, and point to a role of PrC in the representation of faces in a manner that can support memory and perception, and that may apply to other object categories more broadly

Category-Specific Item Recognition and the Medial Temporal Lobe

Much neuropsychological and neuroimaging research has been focused on the contributions of different medial temporal lobe (MTL) structures to recognition memory. The majority of these studies have linked perirhinal cortex (PrC) to item recognition, whereas the hippocampus and parahippocampal cortex (PhC) have primarily been associated with the recollection of contextual detail pertaining to a specific prior stimulus encounter. Here, I report results from three fMRI studies that examined the neural correlates of item recognition with a specific focus on the relationship between such signals and category-specific effects in the MTL. In Chapter 2, I reveal that category-specific representations in both PrC and PhC can be brought to bear on item recognition decisions. In Chapter 3, I examined the specific stimulus properties that determine the relative contributions of PrC and PhC to item recognition, with a focus on landmark suitability. The results from this study revealed item recognition signals for non-landmark objects in PrC and landmarks in PhC. In Chapter 4, I focused specifically on face recognition to characterize the manner in which PrC codes item-recognition signals and to further explore the issue of category-specificity with independent functional localizer data. Results from this study indicate that item recognition signals in PrC can be distributed across voxels with directionally heterogeneous response profiles. Further, these data also revealed that the voxels comprising these patterns respond preferentially to faces under passive viewing conditions. Taken together, these findings suggest that item recognition signals are represented in a distributed, category-specific manner within both PrC and PhC