ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Sleep is regulated by neuronal mechanisms located in both the BRAINSTEM and FOREBRAIN. REM sleep is thought to be induced by the activation of CHOLINERGIC neurons in the MESOPONTINE TEGMENTUM and ACETYLCHOLINE release in the PONTINE RETICULAR FORMATION, which in turn triggers ATONIA and the phasic components of REM sleep. MONOAMINERGIC neurons in the LOCUS COERULEUS and DORSAL RAPHE NUCLEUS are thought to have a permissive role in REM sleep induction, by disinhibiting the cholinergic neurons. At the same time, ascending pathways from the reticular formation activate the THALAMUS and forebrain structures to induce AROUSAL of the CEREBRAL CORTEX. The mechanisms for non-REM sleep are less well understood than for REM sleep. However, the PREOPTIC AREA in the HYPOTHALAMUS and the dorsal reticular formation of the MEDULLA including the NUCLEUSOF THE SOLITARY TRACT are thought to have a role in non-REM sleep. Humoural factors such as HORMONES, CYTOKINES and ADENOSINE have also been implicated in promotion of sleep. Sleep and wakefulness also show daily rhythms, and are controlled by the circadian clock (see BIOLOGICAL CLOCK;
Neuropharmacologic considerations in the treatment of vegetative state and minimally conscious state following brain injury
Mark J. Ashley, David A. Hovda in Traumatic Brain Injury, 2017
Consciousness is a state of awareness dependent upon adequate arousal mechanisms, functioning selective attention, and the ability to perceive and interpret sensory information from the world around us. Arousal, the foundation of consciousness, depends upon multiple connections between the ascending reticular activating system (ARAS) and the cortex via subcortical relay stations. The ARAS originates in the brain stem and exerts its effects on higher cortical centers by way of collateral projections through the thalamus, posterior hypothalamus, and basal forebrain. The brain stem ARAS is comprised of several distinct nuclei that rely on a number of different neurotransmitters to activate rostral brain regions. Thus, redundancy is built into the systems that support our most basic cognitive functions.
The Central Nervous System Organization of Behavior
Rolland S. Parker in Concussive Brain Trauma, 2016
One function of the reticular formation is activation of the brain for behavioral arousal and different levels of awareness. The ARAS consists of the axons of a network extending from the medulla, the upper brainstem (including the midbrain), the hypothalamus, and basal forebrain. It includes the following systems: pedunculopontine, parabrachial, medial raphe, locus ceruleus, tuberomammillary, melanin-concentrating hormones and orexin, and the basal forebrain. Its function is increasing wakefulness and the responsiveness of cortical and thalamic neurons to sensory stimuli (arousal). In contrast to direct sensory pathways through the thalamus, their function is to diffusely innervate the thalamus and cerebral cortex and maintain them in a state in which they can transmit and respond appropriately to incoming sensory information. These pathways innervate the reticular nucleus and intralaminar nuclei of the thalamus. The ARAS divides into two branches at the junction of the midbrain and diencephalon. One branch (direct) enters the thalamus, where it activates and modulates thalamic relay nuclei and intralaminar nuclei with diffuse cortical projections. The other branch (indirect and diffuse) travels through the lateral hypothalamic area to be joined by ascending output from the hypothalamus and basal forebrains. These diffusely innervate the cerebral cortex (Saper, 2000).
Thalamic neuromodulation in epilepsy: A primer for emerging circuit-based therapies
Published in Expert Review of Neurotherapeutics, 2023
Bryan Zheng, David D. Liu, Brian B Theyel, Hael Abdulrazeq, Anna R. Kimata, Peter M Lauro, Wael F. Asaad
The thalamus is likely key to the implementation of state transitions between levels or types of cortical arousal and can maintain those states through broad, course regulation of cortical activity[65–69]. This function is evident in various sleep stages and their distinct thalamocortical signatures. For example, the synchronous transition to ‘down’ states across multiple cortical regions during slow-wave sleep is likely mediated by the midline thalamus[70]. Here, the thalamus appears to be the critical link between brainstem regions involved in arousal, primarily the ascending reticular activating system (RAS), and the cortex. This network serves as a synchronous, broad modulator of cortical processing, and a potential regulator of sleep, alertness, and consciousness[71–73]. So, in addition to being the gatekeeper for specific information trying to gain access to cortex, modulatory projections via the thalamus enforce cortical compliance with brainstem-derived state signals.
Efficacy of neuromuscular electrical stimulation in improving the negative psychological state in patients with cerebral infarction and dysphagia
Published in Neurological Research, 2018
Yanfang Zeng, James Yip, Hongli Cui, Longfei Guan, Haomeng Zhu, Weidong Zhang, Huishan Du, Xiaokun Geng
The above results suggest that NMES combined with swallowing training may improve psychological outcomes in patients with post-stroke dysphagia. The mechanism of improvement with NMES therapy may involve using derived outgoing inhibitory or excitatory stimulation to enter the skin or deeper sensory receivers to conduct through the spinal cord to the brainstem reticular formation. The brainstem reticular formation and cerebral cortex mutually influence each other, and when the activity of the brainstem reticular formation is low, stimulation conducted into the brain cortex will also be reduced. If the activity of the brainstem reticular formation increases, cerebral cortex excitability will be increased, and various psychiatric symptoms and psychological symptoms may also be improved to some extent [31].
Telling the Truth About Pain: Informed Consent and the Role of Expectation in Pain Intensity
Published in AJOB Neuroscience, 2018
Nada Gligorov
The gate control theory of pain postulates a gate control mechanism in the spinal cord (Melzack and Wall 1965). This gate control system modulates the input transmitted from nociceptors to the transmission cells (T cells) located in the dorsal horn of the spinal cord. When the output from the dorsal horn T cells is achieved, it is transmitted toward two distinct brain systems: “(a) via neospinothalamic fibers into the ventrobasal and posterolateral thalamus and somatosensory cortex; and (b) via medially coursing fibers, that comprise a paramedial ascending system, into the reticular formation and medial intralaminar thalamus and the limbic system” (Ronald Melzack and Casey 1968, 427). These two distinct but interacting brain pathways realize the three distinct elements of pain and form the pain matrix in the brain. The pathway that projects into the thalamus and the somatosensory cortex underlies the sensory and discriminative aspects of pain, while the activation of the reticular formation and the limbic system contributes to the unpleasantness of pain and motivates avoidance of noxious stimuli. The cognitive and evaluative element of pain is localized in the neocortical areas of the brain. Based on gate control theory, the cognitive aspects of pain can have an inhibitory effect and can change the output from the dorsal horn, preventing the projection of the pain signal into the brain. Cognitive processes can affect both the sensory and the discriminative aspects of pain, as well as its affective and motivational aspects.