Progress and challenges in probing the human brain

Poldrack, Russell A.; Farah, Martha J.

doi:10.1038/nature15692

Cited by 248 publications

(167 citation statements)

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“…Flexible surface electrode arrays (10)(11)(12) are also capable of mapping activity at the cellular level but are not capable of accessing deeper brain regions and generally have spatial resolution inferior to that of optical imaging. Implantable electrical probes can provide advantages for high-spatiotemporalresolution neural recordings independent of probing depth compared with other techniques (6). However, conventional implanted electrical probes, such as silicon and microwire probes (13,14), generally exhibit immune responses that lead to glial scar formation and neuronal cell depletion at the interfacial tissue/probe region (15)(16)(17)(18).…”

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confidence: 99%

Syringe-injectable mesh electronics integrate seamlessly with minimal chronic immune response in the brain

Zhou

Hong

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

193

211

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Implantation of electrical probes into the brain has been central to both neuroscience research and biomedical applications, although conventional probes induce gliosis in surrounding tissue. We recently reported ultraflexible open mesh electronics implanted into rodent brains by syringe injection that exhibit promising chronic tissue response and recording stability. Here we report time-dependent histology studies of the mesh electronics/brain-tissue interface obtained from sections perpendicular and parallel to probe long axis, as well as studies of conventional flexible thin-film probes. Confocal fluorescence microscopy images of the perpendicular and parallel brain slices containing mesh electronics showed that the distribution of astrocytes, microglia, and neurons became uniform from 2–12 wk, whereas flexible thin-film probes yield a marked accumulation of astrocytes and microglia and decrease of neurons for the same period. Quantitative analyses of 4- and 12-wk data showed that the signals for neurons, axons, astrocytes, and microglia are nearly the same from the mesh electronics surface to the baseline far from the probes, in contrast to flexible polymer probes, which show decreases in neuron and increases in astrocyte and microglia signals. Notably, images of sagittal brain slices containing nearly the entire mesh electronics probe showed that the tissue interface was uniform and neurons and neurofilaments penetrated through the mesh by 3 mo postimplantation. The minimal immune response and seamless interface with brain tissue postimplantation achieved by ultraflexible open mesh electronics probes provide substantial advantages and could enable a wide range of opportunities for in vivo chronic recording and modulation of brain activity in the future.

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mentioning

confidence: 99%

Syringe-injectable mesh electronics integrate seamlessly with minimal chronic immune response in the brain

Zhou

Hong

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

193

211

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“…Current approaches to functional parcellations of the cerebral cortex using fMRI [18] can be grouped into two classes of methods. The first class includes hard parcellations, in which each vertex belongs to exactly one parcel.…”

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confidence: 99%

Inferring Individual-Level Variations in the Functional Parcellation of the Cerebral Cortex

Matthews

Guo

2016

IEEE Trans. Biomed. Eng.

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Abstract-Objective: Functional parcellation of the cerebral cortex is variable across different subjects or between cognitive states. Ignoring individual -or state -dependent variations in the functional parcellation may lead to inaccurate representations of individual functional connectivity, limiting the precision of interpretations of differences in individual connectivity profiles. However, it is difficult to infer the individual-level variations due to the relatively low robustness of methods for parcellation of individual subjects. Methods: We propose a method called "joint K-means" to robustly parcellate the cerebral cortex using functional magnetic resonance imaging (fMRI) data for contrasts between two states or subjects that intended to characterize variance in individual functional parcellations. The key idea of the proposed method is to jointly infer parcellations in contrasted datasets by iterative descent, while constraining the similarity of the two pathways in searches for local minima to reduce spurious variations. Results: Parcellations of resting-state fMRI datasets from the Human Connectome Project show that the similarity of parcellations for an individual subject studied on two sessions is greater than that between different subjects. Differences in parcellations between subjects are non-uniformly distributed across the cerebral cortex, with clusters of higher variance in the prefrontal, lateral temporal and occipito-parietal cortices. This pattern is reproducible across sessions, between groups and using different numbers of parcels. Conclusion: The individual-level variations inferred by the proposed method are plausible and consistent with the previously reported functional connectivity variability. Significance: The proposed method is a promising tool for investigating relationships between the cerebral functional organization and behavioral differences.

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“…While informative, the aforementioned literature (and 'brain-mapping' in general) largely focuses on isolating regions specialised for a particular function, by way of examining discrete regional activation amplitudes Poldrack and Farah, 2015). This approach ignores the fact that brain regions will likely need to work together in concert to achieve complex behavioural outcomes.…”

Section: From Local To Global Models Of Brain Activation Associated Wmentioning

confidence: 99%

“…Popular techniques used to investigate neural dynamics in humans include functional magnetic resonance imaging (fMRI), positron emission tomography (PET), magnetoencephalography (MEG) and electroencephalography (EEG). Since its inception in 1990 (Ogawa et al, 1990) fMRI has arguably become the workhorse of investigations in cognitive neuroscience, largely due to its high spatial resolution (Poldrack and Farah, 2015). A typical, modern fMRI study has a spatial resolution of approximately 2-3 mm 3 and the potential to collect data samples every one to two seconds.…”

Section: Assessing Changes In Human Brain Activity In Vivomentioning

confidence: 99%

“…With the widespread availability of fMRI, GLM became the principal tool for investigating brain function (Poldrack and Farah, 2015). There are various reasons for this, including free and widely available statistical analysis packages (e.g., statistical parametric mapping Friston et al, 1994) and the relative simplicity and flexibility of analysis, as well as the intuitive inferences that can be made from a significant result (e.g., whether a given brain region has a higher BOLD signal, or 'level of activity', in one experimental condition compared with another).…”

Section: Univariate Analysis Of the Bold Signalmentioning

confidence: 99%

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Characterisation of Functional Brain Networks underlying Cognitive Reasoning and Intelligence

Hearne¹

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Intelligence is a general mental capacity that encompasses the ability to plan, problem-solve, reason, think abstractly and comprehend complex relations between concepts. Measured via complex, multistep reasoning tasks, individual differences in intelligence scores are highly predictive of a number of crucial life outcomes. Despite many decades of research, however, the neural bases of intelligence and reasoning abilities are not well understood. Early neuroimaging and lesion studies suggested that regions of the prefrontal cortex are exclusively responsible for intelligent behaviour and higher cognitive reasoning abilities. More recently, however, investigators have conceptualized intelligence as relying upon a widely distributed network of interconnected nodes. The aim of my thesis was to investigate human reasoning and intelligence within this newer, network-centric framework. I conducted a series of functional magnetic resonance imaging (fMRI) experiments to characterize relevant networks in the brain, and related these networks to reasoning task performance, individual differences in intelligence, and the breakdown of reasoning ability amongst individuals with developmental anomalies in brain wiring.The thesis is organized into seven chapters. In the first chapter, I introduce the research question in the context of previous literature that has investigated the brain-basis of reasoning and intelligence by measuring brain activity using fMRI. In doing so, I discuss the origins of intelligence, why task complexity matters, as well as modern in-vivo brain imaging techniques and their biological basis. I then present the concepts of brain network organization, connectivity and graph theory as a relatively untapped avenue to explain higher cognitive reasoning. Armed with this new framework for understanding the brain, I discuss a number of studies that have used this approach to inform the key questions investigated in this thesis.In Chapter 2 I employed an individual-differences approach to investigate the relationship between 'resting-state' baseline functional networks and commonly used measures of intelligence.Previous work has implicated a fronto-parietal network of brain regions that support higher cognitive reasoning, formalized in the parieto-frontal theory of intelligence. However, existing evidence for the fronto-parietal theory is mixed, at least with respect to findings from connectivity studies. To address this issue, I undertook a quantitative summary of previous literature and performed an empirical analysis of data from a large cohort of individuals (N = 317) sourced from the Human Connectome Project. I found that connectivity between the default-mode and fronto-parietal networks best explained individual differences in intelligence.In Chapter 3 I investigated the relationship between default-mode and cognitive control networks during a complex reasoning task. Participants completed a modified version of the classic Wason Selection Task, a measure of relational reasoning, in which the num...

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Progress and challenges in probing the human brain

Cited by 248 publications

References 100 publications

Syringe-injectable mesh electronics integrate seamlessly with minimal chronic immune response in the brain

Syringe-injectable mesh electronics integrate seamlessly with minimal chronic immune response in the brain

Inferring Individual-Level Variations in the Functional Parcellation of the Cerebral Cortex

Characterisation of Functional Brain Networks underlying Cognitive Reasoning and Intelligence

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