Reciprocal anatomical relationship between primary sensory and prefrontal cortices in the human brain

The human brain exhibits remarkable interindividual variability in cortical architecture. Despite extensive evidence for the behavioral consequences of such anatomical variability in individual cortical regions, it is unclear whether and how different cortical regions covary in morphology. Using a novel approach that combined noninvasive cortical functional mapping with whole-brain voxel-based morphometric analyses, we investigated the anatomical relationship between the functionally mapped visual cortices and other cortical structures in healthy humans. We found a striking anticorrelation between the gray matter volume of primary visual cortex and that of anterior prefrontal cortex, independent from individual differences in overall brain volume. Notably, this negative correlation formed along anatomically separate pathways, as the dorsal and ventral parts of primary visual cortex showed focal anticorrelation with the dorsolateral and ventromedial parts of anterior prefrontal cortex, respectively. Moreover, a similar inverse correlation was found between primary auditory cortex and anterior prefrontal cortex, but no anatomical relationship was observed between other visual cortices and anterior prefrontal cortex. Together, these findings indicate that an anatomical trade-off exists between primary sensory cortices and anterior prefrontal cortex as a possible general principle of human cortical organization. This new discovery challenges the traditional view that the sizes of different brain areas simply scale with overall brain size and suggests the existence of shared genetic or developmental factors that contributes to the formation of anatomically and functionally distant cortical regions

Weighting of binocular experience in visual cortical development

After birth the brain adapts to characteristics in the environment in order to optimise its resources with respect to the individual's circumstances. For instance, early monocular deprivation results in reduced cortical representation and visual acuity of the deprived eye. However, such a loss of visual function in one eye after only transient periods of compromised vision through injury or infection would seem to be maladaptive. I examined here whether cortical deprivation effects can be counteracted by daily periods of normal experience. Cats received variable daily regimens of monocular deprivation (by wearing a mask) and binocular exposure. Visual cortex function was subsequently assessed with optical imaging of intrinsic signals, visually evoked potentials, and extracellular electrophysiological recordings. Regardless of the overall length of visual experience, daily binocular vision for as little as 30 minutes, but no less, allowed normal ocular dominance and visual responses to be maintained despite several times longer periods of deprivation. Thus, the absolute amount of daily binocular vision rather than its relative share of the total daily exposure determined the outcome. When 30 minutes binocular exposure were broken up into two 15-minute blocks flanking the deprivation period, ocular dominance resembled that of animals with only 15 minutes binocular vision, suggesting that binocular experience must be continuous to be most effective. My results demonstrate that normal experience is clearly more efficacious in maintaining a binocular visual cortex than abnormal experience is in shifting the ocular dominance distribution. These findings con tribute to the larger debate about how much nature and nurture, respectively, contribute to the development of the brain they suggest that while experience plays a significant role, for some functions there may be an intrinsic bias towards a state that is optimally adapted to the most probable environment.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Weighting of binocular experience in visual cortical development.

After birth the brain adapts to characteristics in the environment in order to optimise its resources with respect to the individual's circumstances. For instance, early monocular deprivation results in reduced cortical representation and visual acuity of the deprived eye. However, such a loss of visual function in one eye after only transient periods of compromised vision through injury or infection would seem to be maladaptive. I examined here whether cortical deprivation effects can be counteracted by daily periods of normal experience. Cats received variable daily regimens of monocular deprivation (by wearing a mask) and binocular exposure. Visual cortex function was subsequently assessed with optical imaging of intrinsic signals, visually evoked potentials, and extracellular electrophysiological recordings. Regardless of the overall length of visual experience, daily binocular vision for as little as 30 minutes, but no less, allowed normal ocular dominance and visual responses to be maintained despite several times longer periods of deprivation. Thus, the absolute amount of daily binocular vision rather than its relative share of the total daily exposure determined the outcome. When 30 minutes binocular exposure were broken up into two 15-minute blocks flanking the deprivation period, ocular dominance resembled that of animals with only 15 minutes binocular vision, suggesting that binocular experience must be continuous to be most effective. My results demonstrate that normal experience is clearly more efficacious in maintaining a binocular visual cortex than abnormal experience is in shifting the ocular dominance distribution. These findings con tribute to the larger debate about how much nature and nurture, respectively, contribute to the development of the brain; they suggest that while experience plays a significant role, for some functions there may be an intrinsic bias towards a state that is optimally adapted to the most probable environment

Dissociable Processes for Orientation Discrimination Learning and Contextual Illusion Magnitude

Previous research suggests an inverse relationship between human orientation discrimination sensitivity and tilt illusion magnitude. To test whether these perceptual functions are inherently linked, we measured both orientation discrimination sensitivity and the magnitude of the tilt illusion before and after participants had been trained for three days on an orientation discrimination task. Discrimination sensitivity improved with training and this improvement remained one month after the initial learning. However, tilt illusion magnitude remained unchanged before and after orientation training, at either trained or untrained orientations. Our results suggest that orientation discrimination sensitivity and illusion magnitude are not inherently linked. They also provide further evidence that, at least for the training periods we employed, perceptual learning of orientation discrimination may involve high-level processes

Bayesian population receptive field modelling

We introduce a probabilistic (Bayesian) framework and associated software toolbox for mapping population receptive fields (pRFs) based on fMRI data. This generic approach is intended to work with stimuli of any dimension and is demonstrated and validated in the context of 2D retinotopic mapping. The framework enables the experimenter to specify generative (encoding) models of fMRI timeseries, in which experimental manipulations enter a pRF model of neural activity, which in turns drives a nonlinear model of neurovascular coupling and Blood Oxygenation Level Dependent (BOLD) response. The neuronal and haemodynamic parameters are estimated together on a voxel-by-voxel or region-of-interest basis using a Bayesian estimation algorithm (variational Laplace). This offers several novel contributions to receptive field modelling. The variance / covariance of parameters are estimated, enabling receptive fields to be plotted while properly representing uncertainty about pRF size and location. Variability in the haemodynamic response across the brain is accounted for. Furthermore, the framework introduces formal hypothesis testing to pRF analysis, enabling competing models to be evaluated based on their model evidence (approximated by the variational free energy), which represents the optimal tradeoff between accuracy and complexity. Using simulations and empirical data, we found that parameters typically used to represent pRF size and neuronal scaling are strongly correlated, which should be taken into account when making inferences. We used the framework to compare the evidence for six variants of pRF model using 7T functional MRI data and we found a circular Difference of Gaussians (DoG) model to be the best explanation for our data overall. We hope this framework will prove useful for mapping stimulus spaces with any number of dimensions onto the anatomy of the brain.Comment: 30 pages, 10 figures. Code available at https://github.com/pzeidman/BayespR

Knowing with Which Eye We See: Utrocular Discrimination and Eye-Specific Signals in Human Visual Cortex

Neurophysiological and behavioral reports converge to suggest that monocular neurons in the primary visual cortex are biased toward low spatial frequencies, while binocular neurons favor high spatial frequencies. Here we tested this hypothesis with functional magnetic resonance imaging (fMRI). Human participants viewed flickering gratings at one of two spatial frequencies presented to either the left or the right eye, and judged which of the two eyes was being stimulated (utrocular discrimination). Using multivoxel pattern analysis we found that local spatial patterns of signals in primary visual cortex (V1) allowed successful decoding of the eye-of-origin. Decoding was above chance for low but not high spatial frequencies, confirming the presence of a bias reported by animal studies in human visual cortex. Behaviorally, we found that reliable judgment of the eye-of-origin did not depend on spatial frequency. We further analyzed the mean response in visual cortex to our stimuli and revealed a weak difference between left and right eye stimulation. Our results are thus consistent with the interpretation that participants use overall levels of neural activity in visual cortex, perhaps arising due to local luminance differences, to judge the eye-of-origin. Taken together, we show that it is possible to decode eye-specific voxel pattern information in visual cortex but, at least in healthy participants with normal binocular vision, these patterns are unrelated to awareness of which eye is being stimulated

Metacognitive ability correlates with hippocampal and prefrontal microstructure

The ability to introspectively evaluate our experiences to form accurate metacognitive beliefs, or insight, is an essential component of decision-making. Previous research suggests individuals vary substantially in their level of insight, and that this variation is related to brain volume and function, particularly in the anterior prefrontal cortex (aPFC). However, the neurobiological mechanisms underlying these effects are unclear, as qualitative, macroscopic measures such as brain volume can be related to a variety of microstructural features. Here we leverage a high-resolution (800 µm isotropic) multi-parameter mapping technique in 48 healthy individuals to delineate quantitative markers of in vivo histological features underlying metacognitive ability. Specifically, we examined how neuroimaging markers of local grey matter myelination and iron content relate to insight as measured by a signal-theoretic model of subjective confidence. Our results revealed a pattern of microstructural correlates of perceptual metacognition in the aPFC, precuneus, hippocampus, and visual cortices. In particular, we extend previous volumetric findings to show that right aPFC myeloarchitecture positively relates to metacognitive insight. In contrast, decreased myelination in the left hippocampus correlated with better metacognitive insight. These results highlight the ability of quantitative neuroimaging to reveal novel brainbehaviour correlates and may motivate future research on their environmental and developmental underpinnings

Do We Need Another Neural Correlate of Contour Integration?

Gilad and colleagues use an elegant combination of voltage-sensitive dyes and high temporal and spatial resolution optical imaging to visualize a differential response to collinear contour elements in monkey V1. This result adds to the literature on the neural correlates of contour integration, but does not yet tackle (or seek to tackle) the question as to whether contour integration is mediated by lateral connections within an area (e.g., V1), through pooling of feedfoward connections, or feedback mechanisms. Moreover, while Gilad et al. find that their differential response is correlated with the behavioral performance of each monkey, there are reasons to suspect that the correlation they observe is a consequence of processing in higher regions, and that the differential V1 response may not play a critical role in integrating contour elements, or in generating the monkey's response. Moreover, this differential V1 response was not observed in a monkey who was not trained on the task, a result that can only be reconciled, if one assumes that the monkey could not see the contour prior to training. If valid, this could raise doubts as to whether the study of contour integration really provides insights into the processes by which normal visual perception is achieved