Dramatic changes to well-known places go unnoticed.

How well do we know our city? It turns out, much more poorly than we might imagine. We used declarative memory and eye-tracking techniques to examine people's ability to detect modifications to real-world landmarks and scenes in Toronto locales with which they have had extensive experience. Participants were poor at identifying which scenes contained altered landmarks, whether the modification was to the landmarks' relative size, internal features, or relation to surrounding context. To determine whether an indirect measure would prove more sensitive, we tracked eye movements during viewing. Changes in overall visual exploration, but not to specific regions of change, were related to participants' explicit endorsement of scenes as modified. These results support the contention that very familiar landmarks are represented at a global or gist level, but not local or fine-grained, level. These findings offer a unified view of memory for gist across verbal and spatial domains, and across recent and remote memory, with implications for hippocampal-neocortical interactions.

Not only memory: Investigating the sensitivity and specificity of the Mnemonic Similarity Task in older adults.

Mnemonic discrimination, the process of distinguishing highly similar items in memory, relies on the dentate gyrus (DG) subregion of the hippocampus. The Mnemonic Similarity Task (MST) has been shown to be a sensitive behavioral measure of mnemonic discrimination that is in wide use (Liu et al., 2016). In this study, we evaluate the sensitivity and specificity of the MST in community-dwelling older adults who were administered the Montreal Cognitive Assessment (MoCA), a well-established screening measure for cognitive impairment. Using regression analyses, we tested a sample of 94 participants to determine whether MoCA overall score, MoCA score without the delayed recall subscale score, MoCA delayed recall subscale score, and MoCA status (MoCA score below or above the cut-off of 26/30) predicted MST lure discrimination performance. Regression models showed that all measures - except the MoCA delayed recall score - were significant predictors of MST lure discrimination performance. Our results support the sensitivity of the MST in detecting general cognitive decline but call into question the specificity of the MST with respect to memory and hippocampal function in a healthy older adult population.

Similarities and differences in the default mode network across rest, retrieval, and future imagining.

The default mode network (DMN) has been identified reliably during rest, as well as during the performance of tasks such as episodic retrieval and future imagining. It remains unclear why this network is engaged across these seemingly distinct conditions, though many hypotheses have been proposed to account for these effects. Prior to generating hypotheses explaining common DMN involvement, the degree of commonality in the DMN across these conditions, within individuals, must be statistically determined to test whether or not the DMN is truly a unitary network, equally engaged across rest, retrieval and future imagining. To provide such a test, we used comparable paradigms (self-directed, uninterrupted thought of equal duration) across the three conditions (rest, retrieval, and future imagining) in a within-participant design. We found lower than expected pattern similarity in DMN functional connectivity across the three conditions. Similarity in connectivity accounted for only 40-50% of the total variance. Partial Least Squares (PLS) analyses revealed the medial temporal regions of the DMN were preferentially coupled with one another during episodic retrieval and future imagining, whereas the non-medial temporal regions of the DMN (e.g., medial prefrontal cortex, lateral temporal cortex, and temporal pole) were preferentially coupled during rest. These results suggest that DMN connectivity may be more flexible than previously considered. Our findings are in line with emerging evidence that the DMN is not a static network engaged commonly across distinct cognitive processes, but is instead a dynamic system, topographically changing in relation to ongoing cognitive demands. Hum Brain Mapp 38:1155-1171, 2017. © 2016 Wiley Periodicals, Inc.

fMRI evidence of equivalent neural suppression by repetition and prior knowledge.

Stimulus repetition speeds behavioral responding (behavioral priming) and is accompanied by suppressed neural responses (repetition suppression; RS) that have been observed up to three days after initial exposure. While some proposals have suggested the two phenomena are linked, behavioral priming has been observed many years after initial exposure, whereas RS is widely considered a transitory phenomenon. This raises the question: what is the true upper limit of RS persistence? To answer this question, we scanned healthy, English-native adults with fMRI as they viewed novel (Asian) proverbs, recently repeated (Asian) proverbs, and previously known (English) proverbs that were matched on various dimensions. We then estimated RS by comparing repeated or previously known proverbs against novel ones. Multivariate analyses linked previously known and repeated proverbs with statistically indistinguishable RS in a broad visual-linguistic network. In each suppressed region, prior knowledge and repetition also induced a common shift in functional connectivity, further underscoring the similarity of the RS phenomenon induced by these conditions. By contrast, activated regions readily distinguished prior knowledge and repetition conditions in a manner consistent with engagement of semantic and episodic memory systems, respectively. Our results illustrate that regardless of whether RS is understood in terms of its magnitude, spatial extent or functional connectivity profile, typical RS effects can be elicited even under conditions where recently triggered biological processes or episodic memory are unlikely to play a prominent role. These results provide important new evidence that RS (of the kind observed after an interval of at least several minutes) reflects the facilitation of perceptual and comprehension processes by any type of information retrieved from long-term memory.

Ill-defined problem solving in amnestic mild cognitive impairment: linking episodic memory to effective solution generation.

It is well accepted that the medial temporal lobes (MTL), and the hippocampus specifically, support episodic memory processes. Emerging evidence suggests that these processes also support the ability to effectively solve ill-defined problems which are those that do not have a set routine or solution. To test the relation between episodic memory and problem solving, we examined the ability of individuals with single domain amnestic mild cognitive impairment (aMCI), a condition characterized by episodic memory impairment, to solve ill-defined social problems. Participants with aMCI and age and education matched controls were given a battery of tests that included standardized neuropsychological measures, the Autobiographical Interview (Levine et al., 2002) that scored for episodic content in descriptions of past personal events, and a measure of ill-defined social problem solving. Corroborating previous findings, the aMCI group generated less episodically rich narratives when describing past events. Individuals with aMCI also generated less effective solutions when solving ill-defined problems compared to the control participants. Correlation analyses demonstrated that the ability to recall episodic elements from autobiographical memories was positively related to the ability to effectively solve ill-defined problems. The ability to solve these ill-defined problems was related to measures of activities of daily living. In conjunction with previous reports, the results of the present study point to a new functional role of episodic memory in ill-defined goal-directed behavior and other non-memory tasks that require flexible thinking. Our findings also have implications for the cognitive and behavioural profile of aMCI by suggesting that the ability to effectively solve ill-defined problems is related to sustained functional independence.

Resting-state functional connectivity of ventral parietal regions associated with attention reorienting and episodic recollection.

In functional neuroimaging studies, ventral parietal cortex (VPC) is recruited by very different cognitive tasks. Explaining the contributions of VPC to these tasks has become a topic of intense study and lively debate. Perception studies frequently find VPC activations during tasks involving attention-reorienting, and memory studies frequently find them during tasks involving episodic recollection. According to the Attention to Memory (AtoM) model, both phenomena can be explained by the same VPC function: bottom-up attention. Yet, a recent functional MRI (fMRI) meta-analysis suggested that attention-reorienting activations are more frequent in anterior VPC, whereas recollection activations are more frequent in posterior VPC. Also, there is evidence that anterior and posterior VPC regions have different functional connectivity patterns. To investigate these issues, we conducted a resting-state functional connectivity analysis using as seeds the center-of-mass of attention-reorienting and recollection activations in the meta-analysis, which were located in the supramarginal gyrus (SMG, around the temporo-parietal junction-TPJ) and in the angular gyrus (AG), respectively. The SMG seed showed stronger connectivity with ventrolateral prefrontal cortex (VLPFC) and occipito-temporal cortex, whereas the AG seed showed stronger connectivity with the hippocampus and default network regions. To investigate whether these connectivity differences were graded or sharp, VLPFC and hippocampal connectivity was measured in VPC regions traversing through the SMG and AG seeds. The results showed a graded pattern: VLPFC connectivity gradually decreases from SMG to AG, whereas hippocampal connectivity gradually increases from SMG to AG. Importantly, both gradients showed an abrupt break when extended beyond VPC borders. This finding suggests that functional differences between SMG and AG are more subtle than previously thought. These connectivity differences can be explained by differences in the input and output to anterior and posterior VPC regions, without the need of postulating markedly different functions. These results are as consistent with integrative accounts of VPC function, such as the AtoM model, as they are with models that ascribe completely different functions to VPC regions.

Highlights and pitfalls of 20 years of application of computerised glow curve analysis to thermoluminescence research and dosimetry.

The technical and dosimetric aspects of computerised glow curve analysis are described in detail including a review of the current 'state-of-the-achieved' in applications to environmental and personal dosimetry, clinical dosimetry, quality control, characterisation of new materials, continuing characterisation of 'old' materials, heavy charged particle dosimetry, mixed field n-gamma dosimetry, X-ray dosimetry and other aspects of thermoluminescence dosimetry. Fearless emphasis is placed on 'pitfalls' as well as successes.

The applicability of the PTTL dose re-analysis method to the Harshaw LiF:Mg,Cu,P material.

The phototransferred thermoluminescence (PTTL) technique is applied to the Harshaw LiF:Mg,Cu,P material. It is demonstrated that using 254-nm UV light, dose levels as low as 0.2 mGy can be re-estimated. The PTTL efficiency was found to be ∼ 6 % in the dose range of 0.2 mGy-1 Gy, and it appears to be dose-independent. This implies that a simple calibration factor could be applied to the PTTL data for the re-estimation of dose levels. It was demonstrated that with a proper choice of the TL readout parameters, and the UV-light irradiation conditions, dose levels that are relevant to personal or environmental dosimetry can be re-estimated.

Uncertainties associated with the use of optically stimulated luminescence in personal dosimetry.

This study investigates several sources of uncertainty associated with the application of optically stimulated luminescence (OSL) to personal dosimetry. A commercial OSL system based on Al(2)O(3):C was used for this study. First, it is demonstrated that the concept of repeated evaluation (readout) of the same dosemeter, often referred to as 're-analysis', can introduce uncertainty in the re-estimated dose. This uncertainty is associated with the fact that the re-analysis process depletes some of the populated traps, resulting in a continuous decrease of the OSL signal with each repeated reading. Furthermore, the rate of depletion may be dose-dependent. Second, it is shown that the previously reported light-induced fading in this system is the result of light leaks through miniature openings in the dosemeter badge.

UV-induced bleaching of deep traps in Harshaw TLD LiF:Mg,Cu,P and LiF:Mg,Ti.

The effects of UV-induced bleaching of deep traps on Harshaw thermoluminescent (TL) LiF:Mg,Cu,P and LiF:Mg,Ti materials were investigated. During a normal heating cycle, LiF:Mg,Cu,P is limited to a maximum temperature of 240 °C. LiF:Mg,Ti can be read to higher temperatures; however, encapsulation in polytetrafluoroethylene limits the maximum readout temperature to 300 °C. Generally, for both materials, these respective temperatures are sufficient for emptying traps corresponding to the main dosemetric peaks. However, when the dosemeters are subjected to a high dose level, such as 1 Gy (much higher than individual monitoring dose levels), higher temperature traps are filled that cannot be emptied without exceeding the above-mentioned maximum temperatures. These high temperature traps tend to be unstable during normal readout and can significantly increase the residual TL signal. The purpose of this study was to investigate the applicability of a UV-induced bleaching technique for emptying higher temperature traps following high-dose applications. In addition, in the case of LiF:Mg,Cu,P, where the maximum readout temperature is significantly lower, we investigated the possibility of reducing the residual signal using the application of repeated readout cycles. The optical bleaching approach was found to be effective in the case of LiF:Mg,Ti; however, for LiF:Mg,Cu,P, no reduction in the residual signal was observed. For this latter material, the application of repeatable readout cycles is very effective and residual signals equivalent to dose levels as low as 0.01 mGy were observed following an initial dose of 5 Gy. To the best of our knowledge, this work is the first attempt to apply an 'optical annealing' technique to the Harshaw thermoluminescent dosemeter (TLD) materials.

The temporal unraveling of autobiographical memory narratives in patients with temporal lobe epilepsy or excisions.

Medial temporal lobe epilepsy (TLE), a condition known to affect the integrity and function of medial temporal lobe structures such as the hippocampus, has been shown to disrupt memory for real-life episodes. Here, patients with unilateral TLE, patients who received a unilateral temporal lobe resection to cure TLE, and healthy controls produced free narratives of autobiographical memories (AMs). To assess temporal resolution, narratives were segmented into bits of information, or details, which were classified according to how precisely they could be located within the time course of the AM. Categories included details corresponding to the entire AM, to parts or subevents within the AM, and to actions taking place within seconds to minutes. The number of details per category was tallied and compared between patients and controls. Temporal order was assessed by determining the correct (internally consistent) chronological order of the sequence of events within the narrative. Results indicate that while patients' memory for the parts or subevents of personal episodes was intact, as was their temporal order, their memory for the minute-by-minute unraveling of the episode was impaired. We believe this loss of temporally specific details may contribute to the reduced vividness of AM recollection in TLE patients. Our findings provide further evidence that patients with hippocampal damage retrieve skeletal AMs for which the gist of the memory is maintained, but the specific details are lost.

Revisiting the novelty effect: when familiarity, not novelty, enhances memory.

Reports of superior memory for novel relative to familiar material have figured prominently in recent theories of memory. However, such novelty effects are incongruous with long-standing observations that familiar items are remembered better. In 2 experiments, we explored whether this discrepancy was explained by differences in the type of familiarity under consideration or by differences in the difficulty of discriminating targets from lures, which may lead to source confusion for familiar but not novel targets. In Experiment 1, we directly tested whether previously observed novelty effects were the result of novelty, discrimination demands, or both. We used linguistic materials (proverbs) to replicate the novelty effect but found that it occurred only when familiar items were subject to source confusion. In Experiment 2, to examine better how novelty influences episodic memory, we used experimentally familiar, pre-experimentally familiar, and novel proverbs in a paradigm designed to overcome discrimination demand confounds. Memory was better for both types of familiar proverbs. These results indicate that familiarity, not novelty, leads to better episodic memory for studied items, regardless of whether familiarity is experimentally induced or based on prior semantic knowledge. We argue that proposals that state that information is encoded better if it is novel are based on over-generalizations of effects arising from the distinctiveness of novel materials.

Hippocampal-neocortical networks differ during encoding and retrieval of relational memory: functional and effective connectivity analyses.

Encoding and retrieval of relational information requires interaction between the hippocampus and various neocortical regions, but it is unknown whether the connectivity of hippocampal-neocortical networks is different at input and output stages. To examine this, we conducted a network analysis of event-related fMRI data collected during a face-recognition, remember/know paradigm. Directed analyses in the medial temporal lobe identified a small region in the left hippocampus that showed differential activation for encoding and retrieval of recollected versus familiar items. Multivariate seed partial least squares (PLS) analysis was used to identify brain regions that were functionally connected to this hippocampal region at encoding and retrieval of 'remembered' items. Anatomically based structural equation modeling (SEM) was then used to test for differences in effective connectivity of network nodes between these two memory stages. The SEM analysis revealed a reversal of directionality between the left hippocampus (LHC) and left inferior parietal cortex (LIPC) at encoding and retrieval. During encoding, activation of the LHC had a positive influence on the LIPC, whereas during retrieval the reverse pattern was found, i.e., the LIPC activation positively influenced LHC activation. These findings emphasize the importance of hippocampal-parietal connections and underscore the complexity of their interactions in initial binding and retrieval/reintegration of relational memory. We also found that, during encoding, the right hippocampus had a positive influence on the right retrospenial cortex, whereas during retrieval this influence was significantly weaker. We submit that examining patterns of connectivity can be important both to elaborate and constrain models of memory involving hippocampal-neocortical interactions.

Encoding the future: successful processing of intentions engages predictive brain networks.

Evidence from cognitive, patient and neuroimaging research indicates that "remembering to remember" intentions, i.e., prospective memory (PM) retrieval, requires both general memory systems involving the medial temporal lobes and an executive system involving rostral PFC (BA 10). However, it is not known how prospective memories are initially formed. Using fMRI, we investigated whether brain activity during encoding of future intentions and present actions differentially predicted later memory for those same intentions (PM) and actions (retrospective memory). We identified two significant patterns of neural activity: a network linked to overall memory and another linked specifically to PM. While overall memory success was predicted by temporal lobe activations that included the hippocampus, PM success was also uniquely predicted by activations in additional regions, including left rostrolateral PFC and the right parahippocampal gyrus. This finding extends the role of these structures to the formation of individual intentions. It also provides the first evidence that PM encoding, like PM retrieval, is supported by both a common episodic memory network and an executive network specifically recruited by future-oriented processing.

Further studies in the reduction of residual in Harshaw TLD-100H (LiF:Mg,Cu,P).

This paper describes further investigations and results in the reduction of residual signal in Harshaw TLD-100H, 600H and 700H (LiF:Mg,Cu,P). TLD-100H is an advanced, relatively new dosimetric material with near tissue-equivalence, flat energy response, and the ability to measure beta, photon and, more importantly, neutrons all from the same base material. The simple glow curve structure provides insignificant fade over extended dosimetric periods of up to 1 y. A criticism of the material has been the residual as compared with TLD-100 (LiF:Mg,Ti). We will show how high-temperature peaks cause the residual signal. We will also show how the various parameters and conditions of the residual measurement technique as well as the configuration of the sample affect the residual measurements. A brief description of the experimental paths taken during our investigation will be presented. We will show how we have reduced the high-temperature peaks of LiF:Mg,Cu,P in our manufacturing process while not affecting other dosimetric properties of this material. The improvements and material properties that need to be shown have been incorporated into our production processes. LiF:Mg,Cu,P stands as a premier choice for personal dosimetry and has been integrated into personal, environmental and extremity configurations of the Harshaw TLD family-line of products.

The application of LiF:Mg,Cu,P to large scale personnel dosimetry: current status and future directions.

LiF:Mg,Cu,P is starting to replace LiF:Mg,Ti in a variety of personnel dosimetry applications. LiF:Mg,Cu,P has superior characteristics as compared to LiF:Mg,Ti including, higher sensitivity, improved energy response for photons, lack of supralinearity and insignificant fading. The use of LiF:Mg,Cu,P in large scale dosimetry programs is of particular interest due to the extreme sensitivity of this material to the maximum readout temperature, and the variety of different dosimetry aspects and details that must be considered for a successful implementation in routine dosimetry. Here we discuss and explain the various aspects of large scale LiF:Mg,Cu,P based dosimetry programs including the properties of the TL material, new generation of TLD readers, calibration methodologies, a new generation of dose calculation algorithms based on the use of artificial neural networks and the overall uncertainty of the dose measurement. The United States Navy (USN) will be the first US dosimetry processor who will use this new material for routine applications. Until June 2002, the Navy used two types of thermoluminescent materials for personnel dosimetry, CaF2:Mn and LiF:Mg,Ti. A program to upgrade the system and to implement LiF:Mg,Cu,P, started in the mid 1990s and was recently concluded. In 2002, the new system replaced the LiF:Mg,Ti and is scheduled to start replacing the CaF2:Mn system in 2006. A pilot study to determine the dosimetric performance of the new LiF:Mg,Cu,P based dosimetry system was recently completed, and the results show the new system to be as good or better than the current system in all areas tested. As a result, LiF:Mg,Cu,P is scheduled to become the primary personnel dosimeter for the entire US Navy in 2006.

A Monte-Carlo code for the detailed simulation of electron and light-ion tracks in condensed matter.

In an effort to understand the basic mechanism of the action of charged particles in solid radiation dosimeters, we extend our Monte-Carlo code (MC4) to condensed media (liquids/solids) and present new track-structure calculations for electrons and protons. Modeling the energy dissipation process is based on a model dielectric function, which accounts in a semi-empirical and self-consistent way for condensed-phase effects which are computationally intractable. Importantly, these effects mostly influence track-structure characteristics at the nanometer scale, which is the focus of radiation action models. Since the event-by-event scheme for electron transport is impractical above several kilo-electron volts, a condensed-history random-walk scheme has been implemented to transport the energetic delta rays produced by energetic ions. Based on the above developments, new track-structure calculations are presented for two representative dosimetric materials, namely, liquid water and silicon. Results include radial dose distributions in cylindrical and spherical geometries, as well as, clustering distributions, which, among other things, are important in predicting irreparable damage in biological systems and prompt electric-fields in microelectronics.

LiF:Mg,Cu,P glow curve shape dependence on heating rate.

The glow curve shape of LiF:Mg,Cu,P (MCP) material is studied in this research. The study is focused on the effects of the heating rate on the dosimetric peaks. Different configurations of dosemeters (chips, cards and powder) are studied. The shifting of the dominant dosimetric peak is observed and analysed. The curves are deconvoluted using the new Harshaw Glow Curve Analyser (GCA) program. Results of the study are presented, as well as possible explanations as to the observed effects.

Discrimination of photon from proton irradiation using glow curve feature extraction and vector analysis.

Two types of thermoluminescence dosemeters (TLDs), the Harshaw LiF:Mg,Ti (TLD-100) and CaF(2):Tm (TLD-300) were investigated for their glow curve response to separate photon and proton irradiations. The TLDs were exposed to gamma irradiation from a (137)Cs source and proton irradiation using a positive ion accelerator. The glow curve peak structure for each individual TLD exposure was deconvolved to obtain peak height, width, and position. Simulated mixed-field glow curves were obtained by superposition of the experimentally obtained single field exposures. Feature vectors were composed of two kinds of features: those from deconvolution and those taken in the neighbourhood of several glow curve peaks. The inner product of the feature vectors was used to discriminate among the pure photon, pure proton and simulated mixed-field irradiations. In the pure cases, identification of radiation types is both straightforward and effective. Mixed-field discrimination did not succeed using deconvolution features, but the peak-neighbourhood features proved to discriminate reliably.

Monte-Carlo calculations of radial dose and restricted-let for protons in water.

A new Monte-Carlo code for event-by-event simulation of the transport of energetic non-relativistic protons (approximately 0.5-10 MeV) and all their secondary electrons (down to 1 Ry) in both the vapour and liquid phases of water is presented. A unified particle-water inelastic model for both phases of water has been developed based on experimental optical data and elements of the Bethe theory. The model applies to both electrons and heavy-charged particles and is particularly suitable for extension to other media of biological relevance (organic polymers, DNA, etc.). Condensed-phase effects are included in the liquid version (MC4L) by means of the dielectric functions which, essentially, substitute the oscillator-strength used in the vapour version (MC4V). The results in the form of radial dose distributions and spatially restricted linear energy transfer are presented and compared with the literature.