scholarly journals From neurons to voxels - repetition suppression is best modelled by local neural scaling

2017 ◽  
Author(s):  
Arjen Alink ◽  
Hunar Abdulrahman ◽  
Richard N. Henson
Keyword(s):  
Computational Models ◽  
Neural Mechanisms ◽  
Functional Magnetic Resonance ◽  
Repetition Effects ◽  
Local Scaling ◽  
Tuning Curves ◽  
Repetition Suppression ◽  
The Difference ◽  
Fmri Adaptation ◽  
Parameter Values

Inferring neural mechanisms from functional magnetic resonance imaging (fMRI) is challenging because the fMRI signal integrates over millions of neurons. One approach is to compare computational models that map neural activity to fMRI responses, to see which best predicts fMRI data. We used this approach to compare four possible neural mechanisms of fMRI adaptation to repeated stimuli (scaling, sharpening, repulsive shifting and attractive shifting), acting across three domains (global, local and remote). Six features of fMRI repetition effects were identified, both univariate and multivariate, from two independent fMRI experiments. After searching over parameter values, only the local scaling model could simultaneously fit all data features from both experiments. Thus fMRI stimulus repetition effects are best captured by down-scaling neuronal tuning curves in proportion to the difference between the stimulus and neuronal preference. These results emphasize the importance of formal modelling for bridging neuronal and fMRI levels of investigation.

scholarly journals Forward models demonstrate that repetition suppression is best modelled by local neural scaling

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Arjen Alink ◽  
Hunar Abdulrahman ◽  
Richard N. Henson
Keyword(s):  
Computational Models ◽  
Neural Mechanisms ◽  
Functional Magnetic Resonance ◽  
Repetition Effects ◽  
Local Scaling ◽  
Tuning Curves ◽  
Repetition Suppression ◽  
The Difference ◽  
Fmri Adaptation ◽  
Parameter Values

Abstract Inferring neural mechanisms from functional magnetic resonance imaging (fMRI) is challenging because the fMRI signal integrates over millions of neurons. One approach is to compare computational models that map neural activity to fMRI responses, to see which best predicts fMRI data. We use this approach to compare four possible neural mechanisms of fMRI adaptation to repeated stimuli (scaling, sharpening, repulsive shifting and attractive shifting), acting across three domains (global, local and remote). Six features of fMRI repetition effects are identified, both univariate and multivariate, from two independent fMRI experiments. After searching over parameter values, only the local scaling model can simultaneously fit all data features from both experiments. Thus fMRI stimulus repetition effects are best captured by down-scaling neuronal tuning curves in proportion to the difference between the stimulus and neuronal preference. These results emphasise the importance of formal modelling for bridging neuronal and fMRI levels of investigation.

Learning Places from Views: Variation in Scene Processing as a Function of Experience and Navigational Ability

2005 ◽  
Vol 17 (1) ◽  
pp. 73-83 ◽  
Author(s):  
Russell A. Epstein ◽  
J. Stephen Higgins ◽  
Sharon L. Thompson-Schill
Keyword(s):  
Functional Magnetic Resonance ◽  
Neural Basis ◽  
Short Term ◽  
Repetition Effects ◽  
Parahippocampal Cortex ◽  
Scene Processing ◽  
Fmri Adaptation ◽  
Over Time

Humans and animals use information obtained from different viewpoints to form representations of the spatial structure of the world. We used functional magnetic resonance imaging (fMRI) adaptation to investigate the neural basis of this learning process and to show how the concomitant representations vary across individuals as a function of navigational ability. In particular, we examined the effect of repeating viewpoint and/ or place information over both short (within-trial) and long (across-scan) intervals on the neural response in scene processing regions. Short-term fMRI adaptation effects in the parahippocampal cortex were initially highly viewpoint-specific but became less so over time. Long-term fMRI repetition effects included a significant viewpoint-invariant component. When individual differences in navigational ability were considered, a significant correlation between the strength of these effects and self-reported navigational competence was observed. In particular, good navigators encoded representations that differed between new and old views and new and old places, whereas bad navigators did not. These results suggest that cortical scene representations evolve over time to become more viewpoint-invariant and that the quality of these representations directly impacts navigational ability.

scholarly journals fMRI-Adaptation and Category Selectivity in Human Ventral Temporal Cortex: Regional Differences Across Time Scales

2010 ◽  
Vol 103 (6) ◽  
pp. 3349-3365 ◽  
Author(s):  
Kevin S. Weiner ◽  
Rory Sayres ◽  
Joakim Vinberg ◽  
Kalanit Grill-Spector
Keyword(s):  
Time Scales ◽  
Medial Axis ◽  
Temporal Cortex ◽  
Neural Mechanism ◽  
Scaling Effects ◽  
Repetition Effects ◽  
Repetition Suppression ◽  
Ventral Temporal Cortex ◽  
Fmri Adaptation ◽  
Anterior Posterior

Repeating object images produces stimulus-specific repetition suppression referred to as functional magnetic resonance imaging-adaptation (fMRI-A) in ventral temporal cortex (VTC). However, the effects of stimulus repetition on functional selectivity are largely unknown. We investigated the effects of short-lagged (SL, immediate) and long-lagged (LL, many intervening stimuli) repetitions on category selectivity in VTC using high-resolution fMRI. We asked whether repetition produces scaling or sharpening of fMRI responses both within category-selective regions as well as in the distributed response pattern across VTC. Results illustrate that repetition effects across time scales vary quantitatively along an anterior-posterior axis and qualitatively along a lateral-medial axis. In lateral VTC, both SL and LL repetitions produce proportional fMRI-A with no change in either selectivity or distributed responses as predicted by a scaling model. Further, there is larger fMRI-A in anterior subregions irrespective of category selectivity. Medial VTC exhibits similar scaling effects during SL repetitions. However, for LL repetitions, both the selectivity and distributed pattern of responses vary with category in medial VTC as predicted by a sharpening model. Specifically, there is larger fMRI-A for nonpreferred categories compared with the preferred category, and category selectivity does not predict fMRI-A across the pattern of distributed response. Finally, simulations indicate that different neural mechanisms likely underlie fMRI-A in medial compared to lateral VTC. These results have important implications for future fMRI-A experiments because they suggest that fMRI-A does not reflect a universal neural mechanism and that results of fMRI-A experiments will likely be paradigm independent in lateral VTC but paradigm dependent in medial VTC.

Two Kinds of fMRI Repetition Suppression? Evidence for Dissociable Neural Mechanisms

2008 ◽  
Vol 99 (6) ◽  
pp. 2877-2886 ◽  
Author(s):  
Russell A. Epstein ◽  
Whitney E. Parker ◽  
Alana M. Feiler
Keyword(s):  
Short Interval ◽  
Brain Regions ◽  
Neural Mechanisms ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Repetition Suppression ◽  
Underlying Mechanisms ◽  
Cortical Regions ◽  
Formal Requirements ◽  
Parahippocampal Place Area

Repetition suppression (RS) is a reduction of neural response that is often observed when stimuli are presented more than once. Many functional magnetic resonance imaging (fMRI) studies have exploited RS to probe the sensitivity of cortical regions to variations in different stimulus dimensions; however, the neural mechanisms underlying fMRI-RS are not fully understood. Here we test the hypothesis that long-interval (between-trial) and short-interval (within-trial) RS effects are caused by distinct and independent neural mechanisms. Subjects were scanned while viewing visual scenes that were repeated over both long and short intervals. Within the parahippocampal place area (PPA) and other brain regions, suppression effects relating to both long- and short-interval repetition were observed. Critically, two sources of evidence indicated that these effects were engendered by different underlying mechanisms. First, long- and short-interval RS effects were entirely noninteractive even although they were measured within the same set of trials during which subjects performed a constant behavioral task, thus fulfilling the formal requirements for a process dissociation. Second, long- and short-interval RS were differentially sensitive to viewpoint: short-interval RS was only significant when scenes were repeated from the same viewpoint while long-interval RS less viewpoint-dependent. Taken together, these results indicate that long- and short-interval fMRI-RS are mediated by different neural mechanisms that independently modulate the overall fMRI signal. These findings have important implications for understanding the results of studies that use fMRI-RS to explore representational spaces.

scholarly journals Antagonism between brain regions relevant for cognitive control and emotional memory facilitates the generation of humorous ideas

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Florian Bitsch ◽  
Philipp Berger ◽  
Andreas Fink ◽  
Arne Nagels ◽  
Benjamin Straube ◽  
...  
Keyword(s):  
Cognitive Control ◽  
Positive Emotions ◽  
Emotional Memory ◽  
Brain Regions ◽  
Neural Mechanisms ◽  
Functional Magnetic Resonance ◽  
Frontal Brain ◽  
Successful Resolution ◽  
Neural Underpinnings ◽  
The Brain

AbstractThe ability to generate humor gives rise to positive emotions and thus facilitate the successful resolution of adversity. Although there is consensus that inhibitory processes might be related to broaden the way of thinking, the neural underpinnings of these mechanisms are largely unknown. Here, we use functional Magnetic Resonance Imaging, a humorous alternative uses task and a stroop task, to investigate the brain mechanisms underlying the emergence of humorous ideas in 24 subjects. Neuroimaging results indicate that greater cognitive control abilities are associated with increased activation in the amygdala, the hippocampus and the superior and medial frontal gyrus during the generation of humorous ideas. Examining the neural mechanisms more closely shows that the hypoactivation of frontal brain regions is associated with an hyperactivation in the amygdala and vice versa. This antagonistic connectivity is concurrently linked with an increased number of humorous ideas and enhanced amygdala responses during the task. Our data therefore suggests that a neural antagonism previously related to the emergence and regulation of negative affective responses, is linked with the generation of emotionally positive ideas and may represent an important neural pathway supporting mental health.

Repetition Suppression of Induced Gamma Activity Predicts Enhanced Orienting toward a Novel Stimulus in 6-month-old Infants

2008 ◽  
Vol 20 (12) ◽  
pp. 2137-2152 ◽  
Author(s):  
Kelly A. Snyder ◽  
Andreas Keil
Keyword(s):  
Visual Processing ◽  
Novelty Detection ◽  
Neural Mechanisms ◽  
Human Infant ◽  
Gamma Activity ◽  
Repeated Stimulus ◽  
Repetition Suppression ◽  
The Face ◽  
Over 40 Years

Habituation refers to a decline in orienting or responding to a repeated stimulus, and can be inferred to reflect learning about the properties of the repeated stimulus when followed by increased orienting to a novel stimulus (i.e., novelty detection). Habituation and novelty detection paradigms have been used for over 40 years to study perceptual and mnemonic processes in the human infant, yet important questions remain about the nature of these processes in infants. The aim of the present study was to examine the neural mechanisms underlying habituation and novelty detection in infants. Specifically, we investigated changes in induced alpha, beta, and gamma activity in 6-month-old infants during repeated presentations of either a face or an object, and examined whether these changes predicted behavioral responses to novelty at test. We found that induced gamma activity over occipital scalp regions decreased with stimulus repetition in the face condition but not in the toy condition, and that greater decreases in the gamma band were associated with enhanced orienting to a novel face at test. The pattern and topography of these findings are consistent with observations of repetition suppression in the occipital–temporal visual processing pathway, and suggest that encoding in infant habituation paradigms may reflect a form of perceptual learning. Implications for the role of repetition suppression in infant habituation and novelty detection are discussed with respect to a biased competition model of visual attention.

scholarly journals Talent in the taxi: a model system for exploring expertise

2009 ◽  
Vol 364 (1522) ◽  
pp. 1407-1416 ◽  
Author(s):  
Katherine Woollett ◽  
Hugo J. Spiers ◽  
Eleanor A. Maguire
Keyword(s):  
Model System ◽  
Neural Mechanisms ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Taxi Drivers ◽  
The Brain ◽  
Use Of Expertise ◽  
Widespread Interest ◽  
Key Questions ◽  
Extensive Practice

While there is widespread interest in and admiration of individuals with exceptional talents, surprisingly little is known about the cognitive and neural mechanisms underpinning talent, and indeed how talent relates to expertise. Because many talents are first identified and nurtured in childhood, it can be difficult to determine whether talent is innate, can be acquired through extensive practice or can only be acquired in the presence of the developing brain. We sought to address some of these issues by studying healthy adults who acquired expertise in adulthood. We focused on the domain of memory and used licensed London taxi drivers as a model system. Taxi drivers have to learn the layout of 25 000 streets in London and the locations of thousands of places of interest, and pass stringent examinations in order to obtain an operating licence. Using neuropsychological assessment and structural and functional magnetic resonance imaging, we addressed a range of key questions: in the context of a fully developed brain and an average IQ, can people acquire expertise to an exceptional level; what are the neural signatures, both structural and functional, associated with the use of expertise; does expertise change the brain compared with unskilled control participants; does it confer any cognitive advantages, and similarly, does it come at a cost to other functions? By studying retired taxi drivers, we also consider what happens to their brains and behaviour when experts stop using their skill. Finally, we discuss how the expertise of taxi drivers might relate to the issue of talent and innate abilities. We suggest that exploring talent and expertise in this manner could have implications for education, rehabilitation of patients with cognitive impairments, understanding individual differences and possibly conditions such as autism where exceptional abilities can be a feature.

fMRI–Adaptation Studies of Viewpoint Tuning in the Extrastriate and Fusiform Body Areas

2010 ◽  
Vol 103 (3) ◽  
pp. 1467-1477 ◽  
Author(s):  
John C. Taylor ◽  
Alison J. Wiggett ◽  
Paul E. Downing
Keyword(s):  
Human Body ◽  
Adaptation Effect ◽  
The Body ◽  
Neural Mechanisms ◽  
Similar Degree ◽  
Neuronal Responses ◽  
Adaptation Studies ◽  
View Invariance ◽  
Cortical Regions ◽  
Fmri Adaptation

People are easily able to perceive the human body across different viewpoints, but the neural mechanisms underpinning this ability are currently unclear. In three experiments, we used functional MRI (fMRI) adaptation to study the view-invariance of representations in two cortical regions that have previously been shown to be sensitive to visual depictions of the human body—the extrastriate and fusiform body areas (EBA and FBA). The BOLD response to sequentially presented pairs of bodies was treated as an index of view invariance. Specifically, we compared trials in which the bodies in each image held identical poses (seen from different views) to trials containing different poses. EBA and FBA adapted to identical views of the same pose, and both showed a progressive rebound from adaptation as a function of the angular difference between views, up to ∼30°. However, these adaptation effects were eliminated when the body stimuli were followed by a pattern mask. Delaying the mask onset increased the response (but not the adaptation effect) in EBA, leaving FBA unaffected. We interpret these masking effects as evidence that view-dependent fMRI adaptation is driven by later waves of neuronal responses in the regions of interest. Finally, in a whole brain analysis, we identified an anterior region of the left inferior temporal sulcus (l-aITS) that responded linearly to stimulus rotation, but showed no selectivity for bodies. Our results show that body-selective cortical areas exhibit a similar degree of view-invariance as other object selective areas—such as the lateral occipitotemporal area (LO) and posterior fusiform gyrus (pFs).

scholarly journals Archie's law – a reappraisal

Solid Earth ◽  
2016 ◽  
Vol 7 (4) ◽  
pp. 1157-1169 ◽  
Author(s):  
Paul W. J. Glover
Keyword(s):  
Systematic Errors ◽  
Apparent Paradox ◽  
Archie’S Law ◽  
A Value ◽  
The Difference ◽  
Reservoir Parameter ◽  
Parameter Values ◽  
Electrical Data ◽  
Extra Parameter ◽  
Better Than

Abstract. When scientists apply Archie's first law they often include an extra parameter a, which was introduced about 10 years after the equation's first publication by Winsauer et al. (1952), and which is sometimes called the “tortuosity” or “lithology” parameter. This parameter is not, however, theoretically justified. Paradoxically, the Winsauer et al. (1952) form of Archie's law often performs better than the original, more theoretically correct version. The difference in the cementation exponent calculated from these two forms of Archie's law is important, and can lead to a misestimation of reserves by at least 20 % for typical reservoir parameter values. We have examined the apparent paradox, and conclude that while the theoretical form of the law is correct, the data that we have been analysing with Archie's law have been in error. There are at least three types of systematic error that are present in most measurements: (i) a porosity error, (ii) a pore fluid salinity error, and (iii) a temperature error. Each of these systematic errors is sufficient to ensure that a non-unity value of the parameter a is required in order to fit the electrical data well. Fortunately, the inclusion of this parameter in the fit has compensated for the presence of the systematic errors in the electrical and porosity data, leading to a value of cementation exponent that is correct. The exceptions are those cementation exponents that have been calculated for individual core plugs. We make a number of recommendations for reducing the systematic errors that contribute to the problem and suggest that the value of the parameter a may now be used as an indication of data quality.

scholarly journals Breeding schemes in reindeer husbandry

Rangifer ◽  
2003 ◽  
Vol 23 (2) ◽  
pp. 45 ◽  
Author(s):  
Lars Rönnegård ◽  
J. A. Woolliams ◽  
Öje Danell
Keyword(s):  
Genetic Gain ◽  
Mass Selection ◽  
Effective Population ◽  
Selection Programme ◽  
Breeding Schemes ◽  
The Difference ◽  
Genetic Contributions ◽  
Parameter Values ◽  
Open Nucleus

The objective of the paper was to investigate annual genetic gain from selection (G), and the influence of selection on the inbreeding effective population size (Ne), for different possible breeding schemes within a reindeer herding district. The breeding schemes were analysed for different proportions of the population within a herding district included in the selection programme. Two different breeding schemes were analysed: an open nucleus scheme where males mix and mate between owner flocks, and a closed nucleus scheme where the males in non-selected owner flocks are culled to maximise G in the whole population. The theory of expected long-term genetic contributions was used and maternal effects were included in the analyses. Realistic parameter values were used for the population, modelled with 5000 reindeer in the population and a sex ratio of 14 adult females per male. The standard deviation of calf weights was 4.1 kg. Four different situations were explored and the results showed: 1. When the population was randomly culled, Ne equalled 2400. 2. When the whole population was selected on calf weights, Ne equalled 1700 and the total annual genetic gain (direct + maternal) in calf weight was 0.42 kg. 3. For the open nucleus scheme, G increased monotonically from 0 to 0.42 kg as the proportion of the population included in the selection programme increased from 0 to 1.0, and Ne decreased correspondingly from 2400 to 1700. 4. In the closed nucleus scheme the lowest value of Ne was 1300. For a given proportion of the population included in the selection programme, the difference in G between a closed nucleus scheme and an open one was up to 0.13 kg. We conclude that for mass selection based on calf weights in herding districts with 2000 animals or more, there are no risks of inbreeding effects caused by selection.

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