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Floris P. De Lange - One of the best experts on this subject based on the ideXlab platform.
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shape perception simultaneously up and downregulates Neural Activity in the primary visual cortex
Current Biology, 2014Co-Authors: Peter Kok, Floris P. De LangeAbstract:Donders Institute for Brain, Cognition and Behaviour,Radboud University Nijmegen, Kapittelweg 29, 6525 ENNijmegen, the NetherlandsSummaryAnessentialpartofvisualperceptionisthegroupingoflocalelements (such as edges and lines) into coherent shapes.Previous studies have shown that this grouping processmodulates Neural Activity in the primary visual cortex (V1)that is signaling the local elements [1–4]. However, thenature of this modulation is controversial. Some studiesfind that shape perception reduces Neural Activity in V1 [2,5, 6], while others report increased V1 Activity during shapeperception [1, 3, 4, 7–10]. Neurocomputational theories thatcast perception as a generative process [11–13] proposethat feedback connections carry predictions (i.e., the gener-ative model), while feedforward connections signal themismatch between top-down predictions and bottom-upinputs.Withinthisframework,theeffectoffeedbackonearlyvisual cortex may be either enhancing or suppressive, de-pendingonwhetherthefeedbacksignalismetbycongruentbottom-up input. Here, we tested this hypothesis by quanti-fying the spatial profile of Neural Activity in V1 during theperception of illusory shapes using population receptivefield mapping. We find that shape perception concurrentlyincreases Neural Activity in regions of V1 that have a recep-tive field on the shape but do not receive bottom-up inputand suppresses Activity in regions of V1 that receivebottom-upinputthatispredictedbytheshape.Theseeffectswere not modulated by task requirements. Together, thesefindingssuggestthatshapeperceptionchangeslower-ordersensory representations in a highly specific and automaticmanner, in line with theories that cast perception in termsof hierarchical generative models.ResultsThe role of early visual regions during shape perception is illunderstood, with some studies reporting Activity suppressiondue to grouping [2, 5, 6] while others report enhancement[1, 3, 4, 7–10]. According to theories that cast perception intermsofhierarchicalgenerativemodels[11–13],NeuralActivityinlower-ordersensoryregionsisdependentbothonwhetheritisdrivenbysensorystimulationandwhetherthisstimulationispredicted on the basis of top-down feedback signals. In thisframework, early visual neurons that do not receive anybottom-up input, but that are predicted to be active becausea shape is inferred at their receptive field location, are ex-pected to show relatively enhanced Neural Activity [3, 4, 8, 9].On the other hand, early visual neurons that receive bottom-up input that is congruent with the shape prediction are ex-pected to show a relatively suppressed response [2, 6, 14].Here, we directly test this framework within the context ofillusory shape perception.Illusory shape perception provides an ideal test bed, as theillusory shape results in both unexpected absence of visualinput (at the location where the shape is perceived but retinalinput is absent) and expected presence of visual input(at the location where the shape provides an explanation forthe bottom-up input). We made use of the well-known illusory‘‘Kanizsa’’ shapes [15], wherein circles with missing wedges(‘‘Pac-Man’’ inducers) are aligned such that they can inducethe perception of an illusory figure (Figure 1A). Using fMRIand population receptive field mapping [16], we quantifiedthe spatial profile of Neural Activity in early visual cortex whilesubjects (n = 20) were presented with stimuli that either did(Figure 1A) or did not (Figure 1B) induce an illusory figure.Moreover, to examine whether effects of shape perceptionwere dependent on attention, we manipulated the focus ofsubjects’ attention. In half of the trials, subjects had to detectthe presence of an occasional illusory diamond (‘‘figure task’’;Figure 1C), placing their attentional focus on the location ofthe illusory shapes. In the other half of the trials, subjectshadtodetecttwotargetletters(XandZ)inarapidlypresentedletter stream at fixation, drawing their attention away from theillusory shapes (‘‘letter task’’).Below, we present the spatially specific responses to thesestimuliinearlyvisualcortexintwodifferentways.First,weesti-mated the population receptive field (pRF) [16] of every voxelin early visual cortex (see Figures S1A–S1C and SupplementalExperimental Procedures available online) and used thisinformation to transform the blood oxygen-level-dependent(BOLD) signal into the reference frame of subjects’ visual fieldof view (Figure S1D; Supplemental Experimental Procedures).Second, we selected groups of voxels based on the locationof their receptive field and averaged over the BOLD signalmeasured in such voxels. In this way, we obtained separateestimates of Neural Activity in regions of primary visual cortex(V1) corresponding to the area of the visual field where theillusory triangles were presented (‘‘figure region’’) and regionscorresponding to the Pac-Man inducers (‘‘inducer region’’;seeSupplementalExperimentalProceduresfordetailsofvoxelselection).Theseanalysisstrategiesarecomplementary:whilethe first method allows for a characterization and visualizationof Neural Activity concurrently for all parts of visual space, thesecond approach is more standard and more easily allowsfor statistical quantification of the experimental effects.Reconstruction of Neural Response to Illusory FiguresWe reconstructed the Neural response evoked by illusory fig-ures (Figure 1A), compared to control stimuli with the samelow-level features but that did not induce an illusory figure(Figure 1B). The results showed a striking spatial dissociation(Figure 2A): Neural Activity for regions of V1 that correspondedto the illusory figure (but not the Pac-Man inducers; figure re-gion) was enhanced when an illusory triangle was present,compared to when the inducers did not form an illusory figure(Figure3A;p<0.001).Inotherwords,theseV1regionsshowedan increased response to the illusory figures, despite the
Brett A Clementz - One of the best experts on this subject based on the ideXlab platform.
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psychosis subgroups differ in intrinsic Neural Activity but not task specific processing
Schizophrenia Research, 2017Co-Authors: Matthew E Hudgenshaney, Lauren E Ethridge, Jennifer E Mcdowell, Sarah K Keedy, Godfrey D Pearlson, Carol A Tamminga, Matcheri S Keshavan, John A Sweeney, Brett A ClementzAbstract:Individuals with psychosis often show high levels of intrinsic, or nonspecific, Neural Activity, but attenuated stimulus-specific Activity. Clementz et al. (2016) proposed that one subgroup of psychosis cases has accentuated intrinsic Activity (Biotype-2's) and a different subgroup (Biotype-1's) has diminished intrinsic Activity, with both groups exhibiting varying degrees of cognitive deficits. This model was studied by assessing Neural Activity in psychosis probands (N=105) during baseline and a 5second period in preparation for a pro-/anti-saccade task. Steady-state stimuli allowed real-time assessment of modulation of visuocortical investment to different target locations. Psychosis probands as a whole showed poor antisaccade performance. As expected, Biotype-1 showed diminished intrinsic Neural Activity and the worst behavior, and Biotype-2 showed accentuated intrinsic Activity and less deviant behavior. Both of these groups also exhibited less dynamic oscillatory phase synchrony. Biotype-3 showed no neurophysiological differences from healthy individuals, despite a history of psychosis. Interestingly, all psychosis subgroups showed normal (i.e., not different from healthy) preparatory modulation of visuocortical investment as a function of cognitive demands, despite varying levels of task performance. Similar analyses conducted subgrouping cases by psychotic symptomatology revealed fewer and less consistent differences, including no intrinsic Activity differences between any clinical subgroup and healthy individuals. This study illustrates that (i) differences in intrinsic Neural Activity may be a fundamental characteristic of psychosis and need to be evaluated separately from stimulus-specific responses, and (ii) grouping patients based on multidimensional classification using neurobiological data may have advantages for resolving heterogeneity and clarifying illness mechanisms relative to traditional psychiatric diagnoses.
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intrinsic Neural Activity differences among psychotic illnesses
Psychophysiology, 2017Co-Authors: Matthew E Hudgenshaney, Lauren E Ethridge, Justin B Knight, Jennifer E Mcdowell, Sarah K Keedy, Godfrey D Pearlson, Carol A Tamminga, Matcheri S Keshavan, John A Sweeney, Brett A ClementzAbstract:Individuals with psychosis have been reported to show either reduced or augmented brain responses under seemingly similar conditions. It is likely that inconsistent baseline-adjustment methods are partly responsible for this discrepancy. Using steady-state stimuli during a pro/antisaccade task, this study addressed the relationship between nonspecific and stimulus-related Neural Activity, and how these activities are modulated as a function of cognitive demands. In 98 psychosis probands (schizophrenia, schizoaffective disorder, and bipolar disorder with psychosis), Neural Activity was assessed during baseline and during a 5-s period in preparation for the pro/antisaccade task. To maximize the ability to identify meaningful differences between psychosis subtypes, analyses were conducted as a function of subgrouping probands by standard clinical diagnoses and neurobiological features. These psychosis “biotypes” were created using brain-based biomarkers, independent of symptomatology (Clementz et al., 2016). Psychosis probands as a whole showed poor antisaccade performance and diminished baseline oscillatory phase synchrony. Psychosis biotypes differed on both behavioral and brain measures, in ways predicted from Clementz et al. (2016). Two biotype groups showed similarly deficient behavior and baseline synchrony, despite diametrically opposed Neural Activity amplitudes. Another biotype subgroup was more similar to healthy individuals on behavioral and brain measures, despite the presence of psychosis. This study provides evidence that (a) consideration of baseline levels of activation and synchrony will be essential for a comprehensive understanding of Neural response differences in psychosis, and (b) distinct psychosis subgroups exhibit reduced versus augmented intrinsic Neural Activity, despite cognitive performance and clinical similarities.
Alan C Evans - One of the best experts on this subject based on the ideXlab platform.
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spontaneous Neural Activity changes after bariatric surgery a resting state fmri study
NeuroImage, 2021Co-Authors: Yashar Zeighami, Sylvain Iceta, Mahsa Dadar, Melissa Pelletier, Melanie Nadeau, Laurent Biertho, Annie Lafortune, Andre Tchernof, Stephanie Fulton, Alan C EvansAbstract:Abstract Background Metabolic disorders associated with obesity could lead to alterations in brain structure and function. Whether these changes can be reversed after weight loss is unclear. Bariatric surgery provides a unique opportunity to address these questions because it induces marked weight loss and metabolic improvements which in turn may impact the brain in a longitudinal fashion. Previous studies found widespread changes in grey matter (GM) and white matter (WM) after bariatric surgery. However, findings regarding changes in spontaneous Neural Activity following surgery, as assessed with the fractional amplitude of low frequency fluctuations (fALFF) and regional homogeneity of Neural Activity (ReHo), are scarce and heterogenous. In this study, we used a longitudinal design to examine the changes in spontaneous Neural Activity after bariatric surgery (comparing pre- to post-surgery), and to determine whether these changes are related to cardiometabolic variables. Methods The study included 57 participants with severe obesity (mean BMI=43.1 ± 4.3 kg/m2) who underwent sleeve gastrectomy (SG), biliopancreatic diversion with duodenal switch (BPD), or Roux-en-Y gastric bypass (RYGB), scanned prior to bariatric surgery and at follow-up visits of 4 months (N = 36), 12 months (N = 29), and 24 months (N = 14) after surgery. We examined fALFF and ReHo measures across 1022 cortical and subcortical regions (based on combined Schaeffer-Xiao parcellations) using a linear mixed effect model. Voxel-based morphometry (VBM) based on T1-weighted images was also used to measure GM density in the same regions. We also used an independent sample from the Human Connectome Project (HCP) to assess regional differences between individuals who had normal-weight (N = 46) or severe obesity (N = 46). Results We found a global increase in the fALFF signal with greater increase within dorsolateral prefrontal cortex, precuneus, inferior temporal gyrus, and visual cortex. This effect was more significant 4 months after surgery. The increase within dorsolateral prefrontal cortex, temporal gyrus, and visual cortex was more limited after 12 months and only present in the visual cortex after 24 months. These increases in Neural Activity measured by fALFF were also significantly associated with the increase in GM density following surgery. Furthermore, the increase in Neural Activity was significantly related to post-surgery weight loss and improvement in cardiometabolic variables, such as blood pressure. In the independent HCP sample, normal-weight participants had higher global and regional fALFF signals, mainly in dorsolateral/medial frontal cortex, precuneus and middle/inferior temporal gyrus compared to the obese participants. These BMI-related differences in fALFF were associated with the increase in fALFF 4 months post-surgery especially in regions involved in control, default mode and dorsal attention networks. Conclusions Bariatric surgery-induced weight loss and improvement in metabolic factors are associated with widespread global and regional increases in Neural Activity, as measured by fALFF signal. These findings alongside the higher fALFF signal in normal-weight participants compared to participants with severe obesity in an independent dataset suggest an early recovery in the Neural Activity signal level after the surgery.
Yashar Zeighami - One of the best experts on this subject based on the ideXlab platform.
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spontaneous Neural Activity changes after bariatric surgery a resting state fmri study
NeuroImage, 2021Co-Authors: Yashar Zeighami, Sylvain Iceta, Mahsa Dadar, Melissa Pelletier, Melanie Nadeau, Laurent Biertho, Annie Lafortune, Andre Tchernof, Stephanie Fulton, Alan C EvansAbstract:Abstract Background Metabolic disorders associated with obesity could lead to alterations in brain structure and function. Whether these changes can be reversed after weight loss is unclear. Bariatric surgery provides a unique opportunity to address these questions because it induces marked weight loss and metabolic improvements which in turn may impact the brain in a longitudinal fashion. Previous studies found widespread changes in grey matter (GM) and white matter (WM) after bariatric surgery. However, findings regarding changes in spontaneous Neural Activity following surgery, as assessed with the fractional amplitude of low frequency fluctuations (fALFF) and regional homogeneity of Neural Activity (ReHo), are scarce and heterogenous. In this study, we used a longitudinal design to examine the changes in spontaneous Neural Activity after bariatric surgery (comparing pre- to post-surgery), and to determine whether these changes are related to cardiometabolic variables. Methods The study included 57 participants with severe obesity (mean BMI=43.1 ± 4.3 kg/m2) who underwent sleeve gastrectomy (SG), biliopancreatic diversion with duodenal switch (BPD), or Roux-en-Y gastric bypass (RYGB), scanned prior to bariatric surgery and at follow-up visits of 4 months (N = 36), 12 months (N = 29), and 24 months (N = 14) after surgery. We examined fALFF and ReHo measures across 1022 cortical and subcortical regions (based on combined Schaeffer-Xiao parcellations) using a linear mixed effect model. Voxel-based morphometry (VBM) based on T1-weighted images was also used to measure GM density in the same regions. We also used an independent sample from the Human Connectome Project (HCP) to assess regional differences between individuals who had normal-weight (N = 46) or severe obesity (N = 46). Results We found a global increase in the fALFF signal with greater increase within dorsolateral prefrontal cortex, precuneus, inferior temporal gyrus, and visual cortex. This effect was more significant 4 months after surgery. The increase within dorsolateral prefrontal cortex, temporal gyrus, and visual cortex was more limited after 12 months and only present in the visual cortex after 24 months. These increases in Neural Activity measured by fALFF were also significantly associated with the increase in GM density following surgery. Furthermore, the increase in Neural Activity was significantly related to post-surgery weight loss and improvement in cardiometabolic variables, such as blood pressure. In the independent HCP sample, normal-weight participants had higher global and regional fALFF signals, mainly in dorsolateral/medial frontal cortex, precuneus and middle/inferior temporal gyrus compared to the obese participants. These BMI-related differences in fALFF were associated with the increase in fALFF 4 months post-surgery especially in regions involved in control, default mode and dorsal attention networks. Conclusions Bariatric surgery-induced weight loss and improvement in metabolic factors are associated with widespread global and regional increases in Neural Activity, as measured by fALFF signal. These findings alongside the higher fALFF signal in normal-weight participants compared to participants with severe obesity in an independent dataset suggest an early recovery in the Neural Activity signal level after the surgery.
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spontaneous Neural Activity changes after bariatric surgery a resting state fmri study
bioRxiv, 2021Co-Authors: Yashar Zeighami, Sylvain Iceta, Mahsa Dadar, Melissa Pelletier, Melanie Nadeau, Laurent Biertho, Annie Lafortune, Andre Tchernof, Stephanie FultonAbstract:1. Abstract Background Metabolic disorders associated with obesity could lead to alterations in brain structure and function. Whether these changes can be reversed after weight loss is unclear. Bariatric surgery provides a unique opportunity to address these questions because it induces marked weight loss and metabolic improvements which in turn may impact the brain in a longitudinal fashion. Previous studies found widespread changes in grey matter (GM) and white matter (WM) after bariatric surgery. However, findings regarding changes in spontaneous Neural Activity following surgery, as assessed with the fractional amplitude of low frequency fluctuations (fALFF) and regional homogeneity of Neural Activity (ReHo), are scarce and heterogenous. In this study, we used a longitudinal design to examine the changes in spontaneous Neural Activity after bariatric surgery (comparing pre- to post-surgery), and to determine whether these changes are related to cardiometabolic variables. Methods The study included 57 participants with severe obesity (mean BMI=43.1±4.3kg/m2) who underwent sleeve gastrectomy (SG), biliopancreatic diversion with duodenal switch (BPD), or Roux-en-Y gastric bypass (RYGB), scanned prior to bariatric surgery and at follow-up visits of 4 months (N=36), 12 months (N=29), and 24 months (N=14) after surgery. We examined fALFF and ReHo measures across 1022 cortical and subcortical regions (based on combined Schaeffer-Xiao parcellations) using a linear mixed effect model. Voxel-based morphometry (VBM) based on T1-weighted images was also used to measure GM density in the same regions. We also used an independent sample from the Human Connectome Project (HCP) to assess regional differences between individuals who had normal-weight (N=46) or severe obesity (N=46). Results We found a global increase in the fALFF signal with greater increase within dorsolateral prefrontal cortex, precuneus, inferior temporal gyrus, and visual cortex. This effect was more significant 4 months after surgery. The increase within dorsolateral prefrontal cortex, temporal gyrus, and visual cortex was more limited after 12 months and only present in the visual cortex after 24 months. These increases in Neural Activity measured by fALFF were also significantly associated with the increase in GM density following surgery. Furthermore, the increase in Neural Activity was significantly related to post-surgery weight loss and improvement in cardiometabolic variables, such as insulin resistance index and blood pressure. In the independent HCP sample, normal-weight participants had higher global and regional fALFF signals, mainly in dorsolateral/medial frontal cortex, precuneus and middle/inferior temporal gyrus compared to the obese participants. These BMI-related differences in fALFF were associated with the increase in fALFF 4 months post-surgery especially in regions involved in control, default mode and dorsal attention networks. Conclusions Bariatric surgery-induced weight loss and improvement in metabolic factors are associated with widespread global and regional increases in Neural Activity, as measured by fALFF signal. These findings alongside the higher fALFF signal in normal-weight participants compared to participants with severe obesity in an independent dataset suggest an early recovery in the Neural Activity signal level after the surgery.
Christof Koch - One of the best experts on this subject based on the ideXlab platform.
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are we aware of Neural Activity in primary visual cortex
Nature, 1995Co-Authors: Francis Crick, Christof KochAbstract:It is usually assumed that people are visually aware of at least some of the neuronal Activity in the primary visual area, V1, of the neocortex. But the neuroanatomy of the macaque monkey suggests that, although primates may be aware of Neural Activity in other visual cortical areas, they are not directly aware of that in area V1. There is some psychophysical evidence in humans that supports this hypothesis.
