Multiscale adaptive smoothing models for the hemodynamic response function in fMRI

In the event-related functional magnetic resonance imaging (fMRI) data analysis, there is an extensive interest in accurately and robustly estimating the hemodynamic response function (HRF) and its associated statistics (e.g., the magnitude and duration of the activation). Most methods to date are developed in the time domain and they have utilized almost exclusively the temporal information of fMRI data without accounting for the spatial information. The aim of this paper is to develop a multiscale adaptive smoothing model (MASM) in the frequency domain by integrating the spatial and frequency information to adaptively and accurately estimate HRFs pertaining to each stimulus sequence across all voxels in a three-dimensional (3D) volume. We use two sets of simulation studies and a real data set to examine the finite sample performance of MASM in estimating HRFs. Our real and simulated data analyses confirm that MASM outperforms several other state-of-the-art methods, such as the smooth finite impulse response (sFIR) model.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS609 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

The Effects of Attention on Age-related Relational Memory Deficits: fMRI Evidence from a Novel Attentional Manipulation

Numerous studies have documented that older adults (OAs) do not perform as well as young adults (YAs) when task demands require the establishment or retrieval of a novel link between previously unrelated information (relational memory: RM). Nonetheless, the source of this age-related RM deficit remains unspecified. One of the most widely investigated factors is an age-related reduction in attentional resources. To investigate this factor, previous researchers have tested whether dividing YAs' attention during encoding equated their RM performance to that of OAs. However, results from these studies failed to replicate the age-related RM impairment observed in aging. The current study investigated whether a reduction in attentional resources for processing of relational information (i.e., relational attention) underlies age-related RM deficits. Using fMRI, we examined whether the effect of reduced attentional resources for processing of relational information is similar to that observed in aging at both behavioral and neural levels. The behavioral results showed that reduced attentional resources for relational information during encoding equated YAs RM performance to that of OAs. Furthermore, the fMRI results demonstrated that both aging, as well as reductions in relational attention in YAs, significantly reduced activity in brain areas associated with successful RM formation, namely, the ventrolateral and dorsolateral PFC, superior and inferior parietal regions, and left hippocampus. Such converging evidence from behavioral and neuroimaging studies suggests that a reduction in attentional resources for relational information is a critical factor for the RM deficit observed in aging

Aged-Related Neural Changes During Memory Conjunction Errors

Human behavioral studies demonstrate that healthy aging is often accompanied by increases in memory distortions or errors. Here we used event-related functional MRI to examine the neural basis of age-related memory distortions. We used the memory conjunction error paradigm, a laboratory procedure known to elicit high levels of memory errors. For older adults, right parahippocampal gyrus showed significantly greater activity during false than during accurate retrieval. We observed no regions in which activity was greater during false than during accurate retrieval for young adults. Young adults, however, showed significantly greater activity than old adults during accurate retrieval in right hippocampus. By contrast, older adults demonstrated greater activity than young adults during accurate retrieval in right inferior and middle prefrontal cortex. These data are consistent with the notion that age-related memory conjunction errors arise from dysfunction of hippocampal system mechanisms, rather than impairments in frontally-mediated monitoring processes.Psycholog

Distinct hippocampal regions make unique contributions to relational memory

Neuroscientific research has shown that the hippocampus is important for binding or linking together the various components of a learning event into an integrated memory. In a prior study, we demonstrated that the anterior hippocampus is involved in memory for the relations among informational elements to a greater extent than it is involved in memory for individual elements (Giovanello, Schnyer, and Verfaellie, 2004). In the current study, we extend those findings by further specifying the role of anterior hippocampus during relational memory retrieval. Specifically, anterior hippocampal activity was observed during flexible retrieval of learned associations, whereas posterior hippocampal activity was detected during reinstatement of study episodes. These findings suggest a functional dissociation across the long axis of human hippocampus based on the nature of the mnemonic process rather than the stage of memory processing or type of stimulus

Remembering what could have happened: Neural correlates of episodic counterfactual thinking

Recent evidence suggests that our capacities to remember the past and to imagine what might happen in the future largely depend on the same core brain network that includes the middle temporal lobe, the posterior cingulate/retrosplenial cortex, the inferior parietal lobe, the medial prefrontal cortex, and the lateral temporal cortex. However, the extent to which regions of this core brain network are also responsible for our capacity to think about what could have happened in our past, yet did not occur (i.e., episodic counterfactual thinking), is still unknown. The present study examined this issue. Using a variation of the experimental recombination paradigm (Addis, Pan, Vu, Laiser, & Schacter, 2009. Neuropsychologia. 47: 2222–2238), participants were asked both to remember personal past events and to envision alternative outcomes to such events while undergoing functional magnetic resonance imaging. Three sets of analyses were performed on the imaging data in order to investigate two related issues. First, a mean-centered spatiotemporal partial least square (PLS) analysis identified a pattern of brain activity across regions of the core network that was common to episodic memory and episodic counterfactual thinking. Second, a non-rotated PLS analysis identified two different patterns of brain activity for likely and unlikely episodic counterfactual thoughts, with the former showing significant overlap with the set of regions engaged during episodic recollection. Finally, a parametric modulation was conducted to explore the differential engagement of brain regions during counterfactual thinking, revealing that areas such as the parahippocampal gyrus and the right hippocampus were modulated by the subjective likelihood of counterfactual simulations. These results suggest that episodic counterfactual thinking engages regions that form the core brain network, and also that the subjective likelihood of our counterfactual thoughts modulates the engagement of different areas within this set of regions.Psycholog

Episodic Memory in Former Professional Football Players with a History of Concussion: An Event-Related Functional Neuroimaging Study

Previous research has demonstrated that sport-related concussions can have short-term effects on cognitive processes, but the long-term consequences are less understood and warrant more research. This study was the first to use event-related functional magnetic resonance imaging (fMRI) to examine long-term differences in neural activity during memory tasks in former athletes who have sustained multiple sport-related concussions. In an event-related fMRI study, former football players reporting multiple sport-related concussions (i.e., three or more) were compared with players who reported fewer than three concussions during a memory paradigm examining item memory (i.e., memory for the particular elements of an event) and relational memory (i.e., memory for the relationships between elements). Behaviorally, we observed that concussion history did not significantly affect behavioral performance, because persons in the low and high concussion groups had equivalent performance on both memory tasks, and in addition, that concussion history was not associated with any behavioral memory measures. Despite demonstrating equivalent behavioral performance, the two groups of former players demonstrated different neural recruitment patterns during relational memory retrieval, suggesting that multiple concussions may be associated with functional inefficiencies in the relational memory network. In addition, the number of previous concussions significantly correlated with functional activity in a number of brain regions, including the medial temporal lobe and inferior parietal lobe. Our results provide important insights in understanding the long-term functional consequences of sustaining multiple sports-related concussions

Differential effects of arousal in positive and negative autobiographical memories

Autobiographical memories are characterized by a range of emotions and emotional reactions. Recent research has demonstrated that differences in emotional valence (positive v. negative emotion) and arousal (the degree of emotional intensity) differentially influence the retrieved memory narrative. Although the mnemonic effects of valence and arousal have both been heavily studied, it is currently unclear whether the effects of emotional arousal are equivalent for positive and negative autobiographical events. In the current study, multilevel models were used to examine differential effects emotional valence and arousal on the richness of autobiographical memory retrieval both between and within subjects. Thirty-four young adults were asked to retrieve personal autobiographical memories associated with popular musical cues and to rate the valence, arousal, and richness of these events. The multilevel analyses identified independent influences of valence and intensity upon retrieval characteristics at the within and between subject levels. In addition, the within subject interactions between valence and arousal highlighted differential effects of arousal for positive and negative memories. These findings have important implications for future studies of emotion and memory, highlighting the importance of considering both valence and arousal when examining the role emotion plays in the richness of memory representation