This article provides insufficient context for those unfamiliar with the subject.(July 2023) |
The dorsal nexus is an area within the dorsal medial prefrontal cortex that serves as an intersection point for multiple brain networks. Research suggests it plays a role in the maintenance and manipulation of information, as well as supporting the control of cognitive functions such as behavior, memory, and conflict resolution. Abnormally increased connectivity between these networks through the dorsal nexus has been associated with certain types of depression. The activity generated by this abnormally high level of connectivity during a depressive state can be identified through magnetic resonance imaging (MRI) and positron emission tomography (PET).
The brain's intrinsic connections are divided into different networks that enable communication between the different structures: The cognitive control network, or executive network (EN), the affective network or somatic network, and the default mode network. [1] These regions are dependent on the dorsal nexus to communicate. [1]
The EN is located in the dorsolateral prefrontal cortex and lateral parietal cortex, and is responsible for the maintenance and manipulation of the information in working memory. The EN also plays an important role as support of adaptive, goal-directed behaviors, which is why it is colloquially referred to as "the problem solver." [2]
The affective (or salience) network includes connections between the limbic area and subcortical areas, and is important during fear and vigilance states, as well as for autonomic and visceral regulation. [2] It also generates the somatic sensations that accompany emotions. [3]
The default mode is most active when the brain is at rest, or when a person is communicating socially. Its activity decreases during the performance of cognitively demanding tasks. [1]
Neuroimaging studies have shown that many neurological diseases and psychiatric disorders are associated with abnormalities in the functional connectivity of neural networks. MRIs indicate that the dorsal nexus is responsible for connecting these networks, and this might explain how symptoms of depression are influenced by the state of brain networks. [1] The increased connectivity can produce symptoms of decreased focus and increased vigilance, which can present as paranoia, rumination or autonomic, visceral and emotional imbalance. [4]
Subjects with depression were observed to have abnormal connectivity in the bilateral parahippocampal cortex, as well as an increase of hyperintensity of white matter. Increased default-mode network connectivity, mediated via a region of the dorsomedial prefrontal cortex, may underline the characteristics of depression. In this pathology, the dorsal nexus is strongly connected to the task-positive, task-negative and affective networks. The function of this node is to allow enhanced “cross-talk” between networks, and this may explain how the diverse symptoms seen in depression converge [5] The dorsal nexus can be related to two different types of depression: decreased and major depression. It is important to mention that there is a big difference between these two types: With decreased depression, the connectivity between the cingulated subgenual cortex and amygdala, pale striatum, and medial thalamus is diminished. In the case of major depression, connectivity is normal. This could explain differences in response to drugs and psychotherapy. [4]
Neuroimaging techniques allow of imaging of the nervous system in vivo, and permit scientists to explore the structures and functions of the human brain. In neuropsychiatry, neuroimaging techniques such as MRI and Positron Emission Tomography allow the identification of different networks that are implicated in various pathologies. [3]
In the case of depression, portions of three different networks (the cognitive control network, the default mode network and the affective network) which are related with conflict resolution, making decisions, behavior, regulate memory and future planning present increased function in MRI’s. These three increased connectivity networks converged specifically on the dorsal nexus. The dorsal nexus has extremely high connectivity with large regions including dorso lateral prefrontal cortex, dorso medial prefrontal cortex, ventral medial prefrontal cortex, pregenual an subgenual cortex, posterior cingulate, and precuneus. Because these networks can be determined for each individual based on the strength of correlation to an a priori seed location, group statistical differences in networks can be evaluated on an image – wide basis. [1]
Treating the symptoms of depression has the purpose of reduce and control the dysfunction that patients could have in any areas of their life. The choice of treatment is based on the needs of the patient and can include drugs, therapy and other similar treatments. Regardless of the chosen treatment, it is necessary to consider possible side effects. [6] In the case of depression associated with dorsal nexus and other associated structures, reducing the increased connectivity might play a critical role reducing depression symptomatology and thus represent a potential therapy target for affective disorders. [7]
Since glutamate is the most abundant and major excitatory neurotransmitter in the brain, pathophysiological changes in glutamatergic signaling are likely to affect neurobehavioral plasticity, information processing and large-scales changes in functional brain connectivity. [7] Ketamine, a fast-acting general anesthetic derived from phencyclidine and use as a pediatric inductor, plays a non-well known role in the neural network dynamics at the healthy brain. The administration of ketamine in abnormal brain has the potential of reduce the increased function of the networks that are seen in depression. The therapeutic potential of ketamine may be explained by reversing disturbances in the glutamatergic system and restoring parts of a disrupted neurobehavioral homeostasis where several structural, metabolic, and functional abnormalities have taken place. [7] Long term ketamine treatments lead to cognitive impairment including problems of short-term memory, visual and verbal memory. On the other hand, short term treatments are generally well tolerated and any damage may be reversible. [6]
Electroconvulsive therapy (ECT) significantly reduces functional connectivity between the dorsolateral prefrontal cortex (Dorsal nexus) and the anterior cingulate cortex, the medial prefrontal cortex, and other areas implicated in major depression. [8] Although electroconvulsive therapy has been used as a treatment for depression since 1930, it has several side effects as loss of memory, confusion and difficulties in forming new memories. Because of this reasons, this kind of treatment is limited to severely damaged patients. [9]
In the human brain, the anterior cingulate cortex (ACC) is the frontal part of the cingulate cortex that resembles a "collar" surrounding the frontal part of the corpus callosum. It consists of Brodmann areas 24, 32, and 33.
In neuroanatomy, the precuneus is the portion of the superior parietal lobule on the medial surface of each brain hemisphere. It is located in front of the cuneus. The precuneus is bounded in front by the marginal branch of the cingulate sulcus, at the rear by the parieto-occipital sulcus, and underneath by the subparietal sulcus. It is involved with episodic memory, visuospatial processing, reflections upon self, and aspects of consciousness.
In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. It is the association cortex in the frontal lobe. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA46, and BA47.
Affective neuroscience is the study of how the brain processes emotions. This field combines neuroscience with the psychological study of personality, emotion, and mood. The basis of emotions and what emotions are remains an issue of debate within the field of affective neuroscience.
Brodmann area 25 (BA25) is the subgenual area, area subgenualis or subgenual cingulate area in the cerebral cortex of the brain and delineated based on its cytoarchitectonic characteristics.
The orbitofrontal cortex (OFC) is a prefrontal cortex region in the frontal lobes of the brain which is involved in the cognitive process of decision-making. In non-human primates it consists of the association cortex areas Brodmann area 11, 12 and 13; in humans it consists of Brodmann area 10, 11 and 47.
The posterior cingulate cortex (PCC) is the caudal part of the cingulate cortex, located posterior to the anterior cingulate cortex. This is the upper part of the "limbic lobe". The cingulate cortex is made up of an area around the midline of the brain. Surrounding areas include the retrosplenial cortex and the precuneus.
Scientific studies have found that different brain areas show altered activity in humans with major depressive disorder (MDD), and this has encouraged advocates of various theories that seek to identify a biochemical origin of the disease, as opposed to theories that emphasize psychological or situational causes. Factors spanning these causative groups include nutritional deficiencies in magnesium, vitamin D, and tryptophan with situational origin but biological impact. Several theories concerning the biologically based cause of depression have been suggested over the years, including theories revolving around monoamine neurotransmitters, neuroplasticity, neurogenesis, inflammation and the circadian rhythm. Physical illnesses, including hypothyroidism and mitochondrial disease, can also trigger depressive symptoms.
In neuroscience, the default mode network (DMN), also known as the default network, default state network, or anatomically the medial frontoparietal network (M-FPN), is a large-scale brain network primarily composed of the dorsal medial prefrontal cortex, posterior cingulate cortex, precuneus and angular gyrus. It is best known for being active when a person is not focused on the outside world and the brain is at wakeful rest, such as during daydreaming and mind-wandering. It can also be active during detailed thoughts related to external task performance. Other times that the DMN is active include when the individual is thinking about others, thinking about themselves, remembering the past, and planning for the future.
The biology of obsessive–compulsive disorder (OCD) refers biologically based theories about the mechanism of OCD. Cognitive models generally fall into the category of executive dysfunction or modulatory control. Neuroanatomically, functional and structural neuroimaging studies implicate the prefrontal cortex (PFC), basal ganglia (BG), insula, and posterior cingulate cortex (PCC). Genetic and neurochemical studies implicate glutamate and monoamine neurotransmitters, especially serotonin and dopamine.
The causes of schizophrenia that underlie the development of schizophrenia, a psychiatric disorder, are complex and not clearly understood. A number of hypotheses including the dopamine hypothesis, and the glutamate hypothesis have been put forward in an attempt to explain the link between altered brain function and the symptoms and development of schizophrenia.
Meditation and its effect on brain activity and the central nervous system became a focus of collaborative research in neuroscience, psychology and neurobiology during the latter half of the 20th century. Research on meditation sought to define and characterize various practices. The effects of meditation on the brain can be broken up into two categories: state changes and trait changes, respectively alterations in brain activities during the act of meditating and changes that are the outcome of long-term practice.
Resting state fMRI is a method of functional magnetic resonance imaging (fMRI) that is used in brain mapping to evaluate regional interactions that occur in a resting or task-negative state, when an explicit task is not being performed. A number of resting-state brain networks have been identified, one of which is the default mode network. These brain networks are observed through changes in blood flow in the brain which creates what is referred to as a blood-oxygen-level dependent (BOLD) signal that can be measured using fMRI.
An identity disturbance is a deficiency or inability to maintain one or more major components of identity. These components include a sense of continuity over time; emotional commitment to representations of self, role relationships, core values and self-standards; development of a meaningful world view; and recognition of one's place in the world.
Neuromorality is an emerging field of neuroscience that studies the connection between morality and neuronal function. Scientists use fMRI and psychological assessment together to investigate the neural basis of moral cognition and behavior. Evidence shows that the central hub of morality is the prefrontal cortex guiding activity to other nodes of the neuromoral network. A spectrum of functional characteristics within this network to give rise to both altruistic and psychopathological behavior. Evidence from the investigation of neuromorality has applications in both clinical neuropsychiatry and forensic neuropsychiatry.
The salience network (SN), also known anatomically as the midcingulo-insular network (M-CIN) or ventral attention network, is a large scale network of the human brain that is primarily composed of the anterior insula (AI) and dorsal anterior cingulate cortex (dACC). It is involved in detecting and filtering salient stimuli, as well as in recruiting relevant functional networks. Together with its interconnected brain networks, the SN contributes to a variety of complex functions, including communication, social behavior, and self-awareness through the integration of sensory, emotional, and cognitive information.
Bipolar disorder is an affective disorder characterized by periods of elevated and depressed mood. The cause and mechanism of bipolar disorder is not yet known, and the study of its biological origins is ongoing. Although no single gene causes the disorder, a number of genes are linked to increase risk of the disorder, and various gene environment interactions may play a role in predisposing individuals to developing bipolar disorder. Neuroimaging and postmortem studies have found abnormalities in a variety of brain regions, and most commonly implicated regions include the ventral prefrontal cortex and amygdala. Dysfunction in emotional circuits located in these regions have been hypothesized as a mechanism for bipolar disorder. A number of lines of evidence suggests abnormalities in neurotransmission, intracellular signalling, and cellular functioning as possibly playing a role in bipolar disorder.
Social cognitive neuroscience is the scientific study of the biological processes underpinning social cognition. Specifically, it uses the tools of neuroscience to study "the mental mechanisms that create, frame, regulate, and respond to our experience of the social world". Social cognitive neuroscience uses the epistemological foundations of cognitive neuroscience, and is closely related to social neuroscience. Social cognitive neuroscience employs human neuroimaging, typically using functional magnetic resonance imaging (fMRI). Human brain stimulation techniques such as transcranial magnetic stimulation and transcranial direct-current stimulation are also used. In nonhuman animals, direct electrophysiological recordings and electrical stimulation of single cells and neuronal populations are utilized for investigating lower-level social cognitive processes.
Network neuroscience is an approach to understanding the structure and function of the human brain through an approach of network science, through the paradigm of graph theory. A network is a connection of many brain regions that interact with each other to give rise to a particular function. Network Neuroscience is a broad field that studies the brain in an integrative way by recording, analyzing, and mapping the brain in various ways. The field studies the brain at multiple scales of analysis to ultimately explain brain systems, behavior, and dysfunction of behavior in psychiatric and neurological diseases. Network neuroscience provides an important theoretical base for understanding neurobiological systems at multiple scales of analysis.
The frontoparietal network (FPN), generally also known as the central executive network (CEN) or, more specifically, the lateral frontoparietal network (L-FPN), is a large-scale brain network primarily composed of the dorsolateral prefrontal cortex and posterior parietal cortex, around the intraparietal sulcus. It is involved in sustained attention, complex problem-solving and working memory.