Andrea Greve

No evidence that 'fast-mapping' benefits novel learning in healthy Older adults

Much evidence suggests that the Hippocampus is necessary for learning novel associations. Contrary to this, Sharon, Moscovitch, and Gilboa (2011) reported four amnesic patients with Hippocampal damage who maintained the capacity to learn novel object-name associations when trained with a ‘fast-mapping’ (FM) technique. This technique therefore potentially offers an alternative route for learning novel information in populations experiencing memory problems. We examined this potential in healthy ageing, by comparing 24 Older and 24 Young participants who completed a FM procedure very similar to Sharon et al. (2011). As expected, the Older group showed worse memory than the Young group under standard explicit encoding (EE) instructions. However, the Older group continued to show worse performance under the FM procedure, with no evidence that FM alleviated their memory deficit. Indeed, performance was worse for the FM than EE condition in both groups. Structural MRI scans confirmed reduced Hippocampal grey-matter volume in the Older group, which correlated with memory performance across both groups and both EE/FM conditions. We conclude FM does not help memory problems that occur with normal ageing, and discuss theoretical implications for memory theories.

Social Cognition Deficits: The Key to Discriminate Behavioral Variant Frontotemporal Dementia from Alzheimer’s Disease Regardless of Amnesia?

Relative sparing of episodic memory is a diagnostic criterion of behavioral variant frontotemporal dementia (bvFTD). However, increasing evidence suggests that bvFTD patients can show episodic memory deficits at a similar level as Alzheimers disease (AD). Social cognition tasks have been proposed to distinguish bvFTD, but no study to date has explored the utility of such tasks for the diagnosis of amnestic bvFTD. Here, we contrasted social cognition performance of amnestic and non-amnestic bvFTD from AD, with a subgroup having confirmed in vivo pathology markers. Ninety-six participants (38 bvFTD and 28 AD patients as well as 30 controls) performed the short Social-cognition and Emotional Assessment (mini-SEA). BvFTD patients were divided into amnestic versus non-amnestic presentation using the validated Free and Cued Selective Reminding Test (FCSRT) assessing episodic memory. As expected, the accuracy of the FCSRT to distinguish the overall bvFTD group from AD was low (69.7% ) with ∼50% of bvFTD patients being amnestic. By contrast, the diagnostic accuracy of the mini-SEA was high (87.9% ). When bvFTD patients were split on the level of amnesia, mini-SEA diagnostic accuracy remained high (85.1% ) for amnestic bvFTD versus AD and increased to very high (93.9% ) for non-amnestic bvFTD versus AD. Social cognition deficits can distinguish bvFTD and AD regardless of amnesia to a high degree and provide a simple way to distinguish both diseases at presentation. These findings have clear implications for the diagnostic criteria of bvFTD. They suggest that the emphasis should be on social cognition deficits with episodic memory deficits not being a helpful diagnostic criterion in bvFTD.

Functional specialisation in the hippocampus and perirhinal cortex during the encoding of verbal associations

Functional magnetic resonance imaging (fMRI) was employed to investigate the contributions of medial temporal lobe (MTL) regions to encoding operations underpinning recollection and familiarity. Participants first studied word pairs. Words in pairs were either weakly or strongly semantically related. In a subsequent retrieval task, participants distinguished between studied pairs, unstudied pairs, and recombined pairs formed from words taken from different studied pairs. Greater activity at encoding for correct judgments to studied pairs with strong, rather than weak, semantic relationships was assumed to index processes supporting subsequent familiarity-based responding. Greater activity for correct judgments to studied pairs than for recombined pairs identified incorrectly as studied pairs was assumed to index processes contributing to recollection-based responding. Evidence that these assumptions were reasonable was obtained in independent behavioural studies, while the outcomes of these fMRI contrasts indicated links between perirhinal cortex and familiarity, and anterior hippocampus and recollection. This functional separation is consistent with models in which the hippocampus and perirhinal cortex support two separable processes that contribute to memories for verbal associations.

The Effects of Hippocampal Lesions on MRI Measures of Structural and Functional Connectivity

Focal lesions can affect connectivity between distal brain regions (connectional diaschisis) and impact the graph‐theoretic properties of major brain networks (connectomic diaschisis). Given its unique anatomy and diverse range of functions, the hippocampus has been claimed to be a critical “hub” in brain networks. We investigated the effects of hippocampal lesions on structural and functional connectivity in six patients with amnesia, using a range of magnetic resonance imaging (MRI) analyses. Neuropsychological assessment revealed marked episodic memory impairment and generally intact performance across other cognitive domains. The hippocampus was the only brain structure exhibiting reduced grey‐matter volume that was consistent across patients, and the fornix was the only major white‐matter tract to show altered structural connectivity according to both diffusion metrics. Nonetheless, functional MRI revealed both increases and decreases in functional connectivity. Analysis at the level of regions within the default‐mode network revealed reduced functional connectivity, including between nonhippocampal regions (connectional diaschisis). Analysis at the level of functional networks revealed reduced connectivity between thalamic and precuneus networks, but increased connectivity between the default‐mode network and frontal executive network. The overall functional connectome showed evidence of increased functional segregation in patients (connectomic diaschisis). Together, these results point to dynamic reorganization following hippocampal lesions, with both decreased and increased functional connectivity involving limbic‐diencephalic structures and larger‐scale networks.

Functional Neuroanatomy Supporting Judgments of When Events Occurred

The neural substrates of memory for when events occurred are not well described. One reason for this is that the paradigms used to date have permitted isolation of only some of the relevant memory processes. In this experiment, functional magnetic resonance imaging was used to identify for the first time brain regions that support two distinct bases upon which “when” judgments can be made. Seventeen human participants (6 male) completed a continuous recognition memory task where the interval between presentation and re-presentation of words varied between 5 and 25 intervening words (the lag). The task on each trial was to distinguish repeated words from those presented for the first time, and to indicate the lag for repeated words. The inferior parietal lobe showed greater activation for shorter lag judgments, regardless of judgment accuracy. The lingual gyrus, by contrast, was more active for correct than for incorrect lag judgments, regardless of the interval between first and second item presentations. Both of these regions have been linked in previous work to the process of recollection, and the findings described here represent a novel neural dissociation across regions that deploy mnemonic information in fundamentally different ways to support judgments about when events occurred.

Does prediction error drive one-shot declarative learning?

Highlights • Role of prediction errors (PE) in human one-shot declarative learning.• PE is manipulated via previous experiences (priors) and sensory inputs (evidence).• PE leads to superior memory across 5 different experiments.• Support for Predictive Interactive Multiple Memory Signals (PIMMS).

Assumptions behind scoring source versus item memory: Effects of age, hippocampal lesions and mild memory problems

Source monitoring paradigms have been used to separate: 1) the probability of recognising an item (Item memory) and 2) the probability of remembering the context in which that item was previously encountered (Source memory), conditional on it being recognised. Multinomial Processing Tree (MPT) models are an effective way to estimate these conditional probabilities. Moreover, MPTs make explicit the assumptions behind different ways to parameterise Item and Source memory. Using data from six independent groups across two different paradigms, we show that one would draw different conclusions about the effects of age, age-related memory problems and hippocampal lesions on Item and Source memory, depending on the use of: 1) standard accuracy calculation vs MPT analysis, and 2) two different MPT models. The MPT results were more consistent than standard accuracy calculations, and furnished additional parameters that can be interpreted in terms of, for example, false recollection or missed encoding. Moreover, a new MPT structure that allowed for separate memory representations (one for item information and one for item-plus-source information; the Source-Item model) fit the data better, and provided a different pattern of significant differences in parameters, than the more conventional MPT structure in which source information is a subset of item information (the Item-Source model). Nonetheless, there is no theory-neutral way of scoring data, and thus proper examination of the assumptions underlying the scoring of source monitoring paradigms is necessary before theoretical conclusions can be drawn.

No effect of hippocampal lesions on stimulus-response bindings

&NA; The hippocampus is believed to be important for rapid learning of arbitrary stimulus‐response contingencies, or S‐R bindings. In support of this, Schnyer et al. (2006) (Experiment 2) measured priming of reaction times (RTs) to categorise visual objects, and found that patients with medial temporal lobe damage, unlike healthy controls, failed to show evidence of reduced priming when response contingencies were reversed between initial and repeated categorisation of objects (a signature of S‐R bindings). We ran a similar though extended object classification task on 6 patients who appear to have selective hippocampal lesions, together with 24 age‐matched controls. Unlike Schnyer et al. (2006), we found that reversing response contingencies abolished priming in both controls and patients. Bayes Factors provided no reason to believe that response reversal had less effect on patients than controls. We therefore conclude that it is unlikely that the hippocampus is needed for S‐R bindings. HighlightsHippocampus is thought important for rapid binding of stimuli (S) and responses (R).Six patients with hippocampal damage showed evidence of normal S‐R bindings.Both patients and controls showed priming of object size judgments.Patients and controls showed equivalent priming reductions when responses reversed.The hippocampus is not necessary for this type of S‐R binding.

Assumptions behind scoring source and item memory impact on conclusions about memory: A reply to Kellen and Singmann's comment (2017).

In our recent article in the journal Cortex (Cooper, Greve, & Henson, 2017), we examined memory for source and item information using data from two different source monitoring paradigms and six different groups of participants. When comparing standard accuracy analysis and various Multinomial Processing Tree (MPT) models, we found that the type of analysis determined the extent to which item and/or source memory differences were found across groups (healthy young and older groups, an older groupwithmildmemory problems, and individuals with hippocampal lesions). Our main point was methodological: that one could draw different conclusions (e.g., whether ageing or hippocampal lesions affect only source memory, or both source and item memory) depending on the analysis used. In our paper, we considered two MPT models that differed in their tree structure. In one of the two models e what we called the “Item-Source” model e the parameter representing accurate source memory occurs “downstream” of the parameter representing accurate item memory. This is the only type of tree structure that we have seen considered in the extensive literature of MPT models of source memory (e.g., Batchelder & Riefer, 1990; Bayen, Murnane, & Erdfelder, 1996; Riefer & Batchelder, 1988), and would seem to correspond to the common assumption that remembering the source in which an item occurred is conditional on remembering the item itself. We contrasted this model with an alternative “Source-Item” model, in which the parameter representing accurate source memory occurs “upstream” of the parameter representing accurate item memory. We likened this to dualprocess models of memory (e.g., Yonelinas, 1999), in which

The missing link? Testing a schema account of unitization

Unitization refers to the creation of a new unit from previously distinct items. The concept of unitization has been used to explain how novel pairings between items can be remembered without requiring recollection, by virtue of new, item-like representations that enable familiarity-based retrieval. We tested an alternative account of unitization – a schema account – which suggests that associations between items can be rapidly assimilated into a schema. We used a common operationalization of “unitization” as the difference between two unrelated words being linked by a definition, relative to two words being linked by a sentence, during an initial study phase. During the following relearning phase, a studied word was re-paired with a new word, either related or unrelated to the original associate from study. In a final test phase, memory for the relearned associations was tested. We hypothesized that, if unitized representations act like schemas, then we would observe some generalization to related words, such that memory would be better in the definition than sentence condition for related words, but not for unrelated words. Contrary to the schema hypothesis, evidence favored the null hypothesis of no difference between definition and sentence conditions for related words (Experiment 1), even when each cue was associated with multiple associates, indicating that the associations can be generalized (Experiment 2), or when the schematic information was explicitly re-activated during Relearning (Experiment 3). These results suggest that unitized associations do not generalize to accommodate new information, and therefore provide evidence against the schema account.