The micro-architecture of the cerebral cortex: Functional neuroimaging models and metabolism

Abstract

In order to interpret/integrate data obtained with different functional neuroimaging modalities (e.g. fMRI, EEG/MEG, PET/SPECT, fNIRS), forward-generative models of a diversity of brain mechanisms at the mesoscopic level are considered necessary. For the cerebral cortex, the brain structure with possibly the most relevance for functional neuroimaging, a variety of such biophysical models has been proposed over the last decade. The development of technological tools to investigate in vitro the physiological, anatomical and biochemical principles at the microscopic scale in comparative studies formed the basis for such theoretical progresses. However, with the most recent introduction of systems to record electrical (e.g. miniaturized probes chronically/acutely implantable in the brain), optical (e.g. two-photon laser scanning microscopy) and atomic nuclear spectral (e.g. nuclear magnetic resonance spectroscopy) signals using living laboratory animals, the field is receiving even greater attention. Major advances have been achieved by combining such sophisticated recording systems with new experimental strategies (e.g. transgenic/knock-out animals, high resolution stereotaxic manipulation systems for probe-guidance and cellular-scale chemical-delivery). Theoreticians may now be encouraged to re-consider previously formulated mesoscopic level models in order to incorporate important findings recently made at the microscopic scale. In this series of reviews, we summarize the background at the microscopic scale, which we suggest will constitute the foundations for upcoming representations at the mesoscopic level. In this first part, we focus our attention on the nerve ending particles in order to summarize basic principles and mechanisms underlying cellular metabolism in the cerebral cortex. It will be followed by two parts highlighting major features in its organization/working-principles to regulate both cerebral blood circulation and neuronal activity, respectively. Contemporary theoretical models for functional neuroimaging will be revised in the fourth part, with particular emphasis in their applications, advantages/limitations and future prospects. However, a wide range of neuroimaging methods have been routinely used to map taskinduced changes in the neuronal activity indirectly reflected in variations of the local 1 BOLD signal calibration by hyperoxia requires additionally measuring PaO2 (partial pressure of oxygen in arterial blood). HHS Public Access Riera et al. Page 2Neuroimage. Author manuscript; available in PMC 2015 March 03. Author Manuscript Author ManuscriptAuthor Manuscript Author Manuscript cerebral perfusion (i.e. functional hyperemia). For many years now, researchers have been trying to elucidate the basic principles underlying this phenomenon and several hypotheses have been formulated so far (see a review by Iadecola 2004). From them the metabolic and neurogenic hypotheses, which arise from answering the question of whether this phenomenon is entirely due to a metabolic deficit or i...

Pitfalls in the dipolar model for the neocortical EEG sources

“…An example of that is the ion pumping by the Na ϩ -K ϩ and Ca 2ϩ ATPases in neurons to reestablish ion gradients after the opening of voltage/chemical-dependent channels. Another example is the glutamate recycling via the EAAT1 and EAAT2 enzyme (Riera et al 2008), which might implicate considerable buffering of ions in the neocortex during an increase of the neuronal activity. These principal buffering systems may also contribute to a redistribution of the electric charge across the cellular membranes regardless of the principle of current conservation.…”

Dynamic causal modelling: A critical review of the biophysical and statistical foundations

“…implantable miniaturized probes) and optical (e.g. two-photon laser scanning microscopy) signals are likely to be very useful for such an experimental validation (Riera et al, 2008).…”

Microvascular Oxygen Tension and Flow Measurements in Rodent Cerebral Cortex during Baseline Conditions and Functional Activation

“…Although it has long been presumed that oxidative metabolism is the primary mechanism to satisfy the brain's energetic demands, the influence and dynamics of oxygen supply remain ambiguous (Bartlett et al, 2008;Riera et al, 2008). During both resting and activated conditions, the blood's supply of oxygen exceeds the brain's energetic demand.…”