The neurobiology of sleep
Philip N. Murphy in The Routledge International Handbook of Psychobiology, 2018
A temporal organization is observed in all animal species – from single-cell organisms to mammals. The most common component of these time-domain changes is a regular transition from an active state to a resting state. The resting state is referred to as “sleep” when the following behavioral features are present: (i) behavioral quiescence, (ii) an increased arousal threshold, (iii) rapid reversibility (for the transition to wakefulness), and (iv) a species-specific location and posture. Sleep states have been clearly evidenced in mammals, birds and reptiles, and there is a growing body of evidence for sleep-like states in amphibians, fishes and even some invertebrates (Hartse, 2011; McNamara et al., 2008). However, the presence of several different states within sleep has only been conclusively documented for warm-blooded vertebrates (mammals and birds). As detailed below, each of these states is associated with a characteristic pattern of brain activity and is accompanied by specific autonomic and behavioral signs. The occurrence of sleep depends on both circadian organization and homeostatic regulation (Borbély, Daan, Wirz-Justice, & Deboer, 2016). Circadian rhythms define the duration and position of sleep during the 24-hour period, modulated by synchronizers, such as meal-time regularity and bed time in humans, whereas homeostatic regulation generates sleep pressure as a function of the time spent awake. In humans, sleep is constituted by three to six 90- to 120-minute cycles per night.
fMRI as a Biomarker in Neuroimaging
Yu Chen, Babak Kateb in Neurophotonics and Brain Mapping, 2017
For the past 10 years, fMRI based on imaging of the endogenous BOLD contrast (Kwong et al. 1992) has been suggested to be a very important tool for exploring brain function during complex cognitive processes such as memory consolidation in humans (Stern et al. 1996; Gabrieli et al. 1997; Brewer et al. 1998). For example, these fMRI studies, together with several other related studies, have confirmed the central role of the medial temporal lobe structures, in other words, the hippocampus and neighboring parahippocampal cortices, in encoding new events into long-term memory (Eichenbaum 2000; Scoville and Milner 2000). Typically, fMRI experiments compare the BOLD signal during one cognitive condition (e.g., encoding new information) to a control task (e.g., viewing learned information) or to a passive baseline condition (e.g., fixed cross). This can be done using “block design” paradigms, in which cognitively similar kinds of stimuli are grouped together in blocks usually lasting 20–40 s, or using “event-related” paradigms, in which single stimuli from different cognitive conditions are randomly presented. In addition to fMRI studies during task performance, there has recently been considerable interest in exploring neuronal activity during awake resting state, also called the “default mode” activity of the human brain (Raichle and Mintun 2006; Horovitz et al. 2009).
Magnetic Resonance Imaging
Shoogo Ueno in Bioimaging, 2020
Block design, event-related design, and resting state are the three main approaches by which brain activity is induced and then measured. In block design, the blocks that continuously produce brain activity by providing stimulation over several consecutive seconds or minutes to test subjects and the subsequent blocks that do not provide stimulation for several seconds or minutes are alternately arranged. The MRI signals between these two blocks are statistically analyzed, and then, the regions presenting significant differences are extracted. In event-related design, one-time stimulation is delivered, and subsequently, MRI signal responses, including time changes, are acquired. Thereafter, second-time or further stimulation is delivered with sufficient intervals. The advantage of this method is that timely information is also acquired. Resting state is a technique that was established recently. It deals with brain activity that is spontaneously produced without any particular external stimulation. Focusing on periodic fluctuations in individual voxel BOLD signals in places with spontaneously occurring activity enables the extraction of combinations of voxels with high correlation to these periodic fluctuations. A high correlation means some type of coupling between neurons, making it possible to locate neural network structures in the brain from measured results.
Resting-state fMRI reveals increased functional connectivity in the cerebellum but decreased functional connectivity of the caudate nucleus in Parkinson’s disease
Published in Neurological Research, 2020
Oliver Kaut, Clemens Mielacher, René Hurlemann, Ullrich Wüllner
Recent studies have emphasized the role of the cerebellum in PD [8]. Functional magnetic resonance imaging (fMRI) studies have found support for the long-held notion that relatively intact cerebellar circuits may compensate for impaired basal ganglia function and that cerebellar activity is increased in PD patients compared to healthy subjects [9]. To assess neural activity, resting-state fMRI [rs-fMRI] has been widely used over the last decade in various neurodegenerative disorders. The objective of resting-state experiments is to assess the statistical properties of endogenously generated neural activity, while the subject is at ‘rest’, which is defined as a constant condition without external stimuli or tasks [10]. In comparison to task-based fMRI, rs-fMRI is not biased by compliance or task performance [11].
HD-tDCS as a neurorehabilitation technique for a case of post-anoxic leukoencephalopathy
Published in Neuropsychological Rehabilitation, 2022
Sarah Garcia, Benjamin M. Hampstead
Anatomical and resting state images were collected through a GE MR750 3 T magnetic resonance system (GE, Milwaukee, WI) with a 32-channel phased array head coil. Sequence parameters for anatomical acquisition were: Field of view (FOV) = 256, Matrix = 256 × 256, 156 slices per volume, 1 × 1 × 1 mm voxel size, TR = 12 ms, TE = 5 ms, TI = 500 ms, flip angle = 15°. For functional resting state data, PT1 was instructed to focus his gaze on a fixation cross (i.e., eyes open) on the screen and not to fall asleep. Resting state data were acquired through a multiband echo planar imaging (EPI) sequence with parameters: FOV = 240, Matrix = 74 × 74, 45 slices per volume, 3.24 × 3.24 × 3 mm voxel size, TR = 900 ms, TE = 30 ms, flip angle = 70°. We acquired 512 volumes but dropped the first 6 to allow for signal normalization, resulting in a total of 7′35.4″ of resting state data.
Examining the relationship between perinatal depression and neurodevelopment in infants and children through structural and functional neuroimaging research
Published in International Review of Psychiatry, 2019
Christy Duan, Megan M. Hare, Morganne Staring, Kristina M. Deligiannidis
Functional MRI (fMRI) measures cerebral blood-oxygenation-level dependent (BOLD) changes in the brain that are tightly correlated to changes in neural activity. Neural co-activation patterns among anatomically separate brain regions is known as functional connectivity (Logothetis, Pauls, Augath, Trinath, & Oeltermann, 2001; van den Heuvel & Hulshoff Pol, 2010). fMRI studies may either measure functional connectivity while the subject completes a designated task (task-based fMRI) or while the subject is at rest (resting-state fMRI) (Bandettini, 2009). These fMRI methods enable observation of distinct brain networks, which are groups of brain areas and neural systems that are active together and, thus, exhibit connectivity (van den Heuvel & Hulshoff Pol, 2010). It is important to note that, while MR is an exciting, non-invasive technique allowing researchers to better understand brain developmental in infants and young children, there are limitations. For example, infant brain MRI white–gray contrast changes over the first 12 months of age and beyond. Many imaging pre-processing steps need to infant-tailored. Further, image analysis tools used for processing and analyzing adult brain MR data can be inadequate for infants, although new computational techniques have been developed and are being refined (Li et al., 2018).
Related Knowledge Centers
- Brain Mapping
- Cerebral Circulation
- Default Mode Network
- Electroencephalography
- Functional Magnetic Resonance Imaging
- Neurological Disorder
- Brain
- Blood-Oxygen-Level-Dependent Imaging
- Mental Disorder
- Magnetic Resonance Imaging