Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

Functional neuroimaging studies have started unravelling unexpected functional attributes for the posteromedial portion of the parietal lobe, the precuneus. This cortical area has traditionally received little attention, mainly because of its hidden location and the virtual absence of focal lesion studies. However, recent functional imaging findings in healthy subjects suggest a central role for the precuneus in a wide spectrum of highly integrated tasks, including visuo-spatial imagery, episodic memory retrieval and self-processing operations, namely first-person perspective taking and an experience of agency. Furthermore, precuneus and surrounding posteromedial areas are amongst the brain structures displaying the highest resting metabolic rates (hot spots) and are characterized by transient decreases in the tonic activity during engagement in non-self-referential goal-directed actions (default mode of brain function). Therefore, it has recently been proposed that precuneus is involved in the interwoven network of the neural correlates of self-consciousness, engaged in self-related mental representations during rest. This hypothesis is consistent with the selective hypometabolism in the posteromedial cortex reported in a wide range of altered conscious states, such as sleep, drug-induced anaesthesia and vegetative states. This review summarizes the current knowledge about the macroscopic and microscopic anatomy of precuneus, together with its wide-spread connectivity with both cortical and subcortical structures, as shown by connectional and neurophysiological findings in non-human primates, and links these notions with the multifaceted spectrum of its behavioural correlates. By means of a critical analysis of precuneus activation patterns in response to different mental tasks, this paper provides a useful conceptual framework for matching the functional imaging findings with the specific role(s) played by this structure in the higher-order cognitive functions in which it has been implicated. Specifically, activation patterns appear to converge with anatomical and connectivity data in providing preliminary evidence for a functional subdivision within the precuneus into an anterior region, involved in self-centred mental imagery strategies, and a posterior region, subserving successful episodic memory retrieval.

/pdf/the-precuneus-a-review-of-its-functional-anatomy-and-q9xsn3nfnb.pdf

The precuneus: a review of its functional anatomy and behavioural correlates.

Over more than a century of research has established the fact that sleep benefits the retention of memory. In this review we aim to comprehensively cover the field of "sleep and memory" research by providing a historical perspective on concepts and a discussion of more recent key findings. Whereas initial theories posed a passive role for sleep enhancing memories by protecting them from interfering stimuli, current theories highlight an active role for sleep in which memories undergo a process of system consolidation during sleep. Whereas older research concentrated on the role of rapid-eye-movement (REM) sleep, recent work has revealed the importance of slow-wave sleep (SWS) for memory consolidation and also enlightened some of the underlying electrophysiological, neurochemical, and genetic mechanisms, as well as developmental aspects in these processes. Specifically, newer findings characterize sleep as a brain state optimizing memory consolidation, in opposition to the waking brain being optimized for encoding of memories. Consolidation originates from reactivation of recently encoded neuronal memory representations, which occur during SWS and transform respective representations for integration into long-term memory. Ensuing REM sleep may stabilize transformed memories. While elaborated with respect to hippocampus-dependent memories, the concept of an active redistribution of memory representations from networks serving as temporary store into long-term stores might hold also for non-hippocampus-dependent memory, and even for nonneuronal, i.e., immunological memories, giving rise to the idea that the offline consolidation of memory during sleep represents a principle of long-term memory formation established in quite different physiological systems.

https://www.zora.uzh.ch/id/eprint/77770/1/physiol_rev_93.pdf

About sleep's role in memory

http://www.unicog.org/publications/DehaeneChangeux_ReviewConsciousness_Neuron2011.pdf

Experimental and Theoretical Approaches to Conscious Processing

Nine previous positron emission tomography (PET) studies of human visual information processing were reanalyzed to determine the consistency across experiments of blood flow decreases during active tasks relative to passive viewing of the same stimulus array. Areas showing consistent decreases during active tasks included posterior cingulate/precuneous (Brodmann area, BA 31/7), left (BAS 40 and 39/19) and right (BA 40) inferior parietal cortex, left dorsolateral frontal cortex (BA S), left lateral inferior frontal cortex (BA 10/47), left inferior temporal gyrus @A 20), a strip of medial frontal regions running along a dorsal-ventral axis (BAs 8, 9, 10, and 32), and the right amygdala.

Experiments involving language-related processes tended to show larger decreases than nonlanguage experiments. This trend mainly reflected blood flow increases at certain areas in the passive conditions of the language experiments (relative to a fixation control in which no task stimulus was present) and slight blood flow decreases in the passive conditions of the nonlanguage experiments. When the active tasks were referenced to the fixation condition, the overall size of blood flow decreases in language and nonlanguage tasks were the same, but differences were found across cortical areas. Decreases were more pronounced in the posterior cingulate/precuneous (BAS 31/7) and right inferior parietal cortex (BA 40) during language-related tasks and more pronounced in left inferior frontal cortex (BA 10/47) during nonlanguage tasks.

Blood flow decreases did not generally show significant differences across the active task states within an experiment, but a verb-generation task produced larger decreases than a read task in right and left inferior parietal lobe (BA 40) and the posterior cingulate/precuneous (BA 31/7), while the read task produced larger decreases in left lateral inferior frontal cortex (BA 10/47). These effects mirrored those found between experiments in the language-nonlanguage comparison.

Consistent active minus passive decreases may reflect decreased activity caused by active task processes that generalize over tasks or increased activity caused by passive task processes that are suspended during the active tasks. Increased activity during the passive condition might reflect ongoing processes, such as unconstrained verbally mediated thoughts and monitoring of the external environment, body, and emotional state.

/pdf/common-blood-flow-changes-across-visual-tasks-ii-decreases-4r2u5i1njk.pdf

Common blood flow changes across visual tasks: Ii. decreases in cerebral cortex

RAPID-EYE-MOVEMENT (REM) sleep is associated with intense neuronal activity, ocular saccades, muscular atonia and dreaming1,2. The function of REM sleep remains elusive and its neural correlates have not been characterized precisely in man. Here we use positron emission tomography and statistical parametric mapping to study the brain state associated with REM sleep in humans. We report a group study of seven subjects who maintained steady REM sleep during brain scanning and recalled dreams upon awakening. The results show that regional cerebral blood flow is positively correlated with REM sleep in pontine tegmentum, left thalamus, both amygdaloid complexes, anterior cingulate cortex and right parietal operculum. Negative correlations between regional cerebral blood flow and REM sleep are observed bilaterally, in a vast area of dorsolateral prefrontal cortex, in parietal cortex (supramarginal gyrus) as well as in posterior cingulate cortex and precuneus. Given the role of the amygdaloid complexes in the acquisition of emotionally influenced memories, the pattern of activation in the amygdala and the cortical areas provides a biological basis for the processing of some types of memory during REM sleep.

Functional neuroanatomy of human rapid-eye-movement sleep and dreaming.

The distribution of regional cerebral blood flow (rCBF) was estimated during sleep and wakefulness by using H215O positron emission tomography (PET) and statistical parametric mapping. A group analysis on 11 good sleepers (8 with steady slow wave sleep, SWS) showed a significant negative correlation between the occurrence of SWS and rCBF in dorsal pons and mesencephalon, thalami, basal ganglia, basal forebrain/hypothalamus, orbitofrontal cortex, anterior cingulate cortex, precuneus, and, on the right side, in a region that follows the medial aspect of the temporal lobe. Given the known decrease in global cerebral blood flow levels during SWS, these negative correlations suggest that rCBF is decreased significantly more in these cerebral areas than in the rest of the brain. The marked rCBF decreases in the pons, mesencephalon, thalamic nuclei, and basal forebrain reflect their close implication in the generation of SWS rhythms. The influence of these rhythms on the telencephalon usually are thought to be global and homogeneous. In contrast, our results show that rCBF is decreased more in some cortical areas (especially in orbitofrontal cortex) than in the rest of the cortex. We hypothesize that cellular processes taking place during SWS might be modulated differently in these regions. Given the functions of the ventromedial frontal areas, we surmise that SWS might be particularly critical for the adaptation of behavior to environmental pressures. This hypothesis is supported indirectly by results of sleep deprivation experiments.

https://www.jneurosci.org/content/jneuro/17/8/2807.full.pdf

Functional neuroanatomy of human slow wave sleep.

Keywords:

muscular blood flow;
positron emission tomography;
nuclear magnetic resonance

/pdf/a-positron-emission-tomography-study-of-voluntarily-and-hocyvrvfn4.pdf

A Positron Emission Tomography Study of Voluntarily and Electrically Contracted Human Quadriceps

Production of oxygen-15, nitrogen-13 and carbon-11 and of their low molecular weight derivatives for biomedical applications

An automated continuous flow process has been developed for the synthesis of11C-ethanol and11C-butanol. These alcohols were synthesized via the same route. The reaction of11CO2 with methylmagnesium bromide or with n-propylmagnesium chloride, followed by a lithium aluminum hydride reduction and hydrolysis produced respectively11C-ethanol and11C-butanol. Preparation can be completed in 25 min. In each case the radiochemical purity, as determined by high pressure liquid chromatography /HPLC/ was greater than 98%. Biological quality control shows that the products are suitable for human use. The process has been completely automated to limit radiation exposure to personnel, reduce preparation time, and increase reproducibility.

J.M. Peters

Papers

Functional neuroanatomy of human rapid-eye-movement sleep and dreaming.

Functional neuroanatomy of human slow wave sleep.

A Positron Emission Tomography Study of Voluntarily and Electrically Contracted Human Quadriceps

Production of oxygen-15, nitrogen-13 and carbon-11 and of their low molecular weight derivatives for biomedical applications

Automated preparation of carbon-11 ethanol and carbon-11 butanol for human studies using positron emission tomography