White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution of action potentials, acting as a relay and coordinating communication between different brain regions.
Binswanger's disease, also known as subcortical leukoencephalopathy and subcortical arteriosclerotic encephalopathy, is a form of small-vessel vascular dementia caused by damage to the white brain matter. White matter atrophy can be caused by many circumstances including chronic hypertension as well as old age. This disease is characterized by loss of memory and intellectual function and by changes in mood. These changes encompass what are known as executive functions of the brain. It usually presents between 54 and 66 years of age, and the first symptoms are usually mental deterioration or stroke.
Frontotemporal dementia (FTD), or frontotemporal degeneration disease, or frontotemporal neurocognitive disorder, encompasses several types of dementia involving the progressive degeneration of frontal and temporal lobes. FTDs broadly present as behavioral or language disorders with gradual onsets. Common signs and symptoms include significant changes in social and personal behavior, apathy, blunting of emotions, and deficits in both expressive and receptive language. Currently, there is no cure for FTD, but there are treatments that help alleviate symptoms.
Normal-pressure hydrocephalus (NPH), also called malresorptive hydrocephalus, is a form of communicating hydrocephalus in which excess cerebrospinal fluid (CSF) occurs in the ventricles, and with normal or slightly elevated cerebrospinal fluid pressure. As the fluid builds up, it causes the ventricles to enlarge and the pressure inside the head to increase, compressing surrounding brain tissue and leading to neurological complications. The disease presents in a classic triad of symptoms, which are memory impairment, urinary frequency, and balance problems/gait deviations. The disease was first described by Salomón Hakim and Adams in 1965.
Semantic dementia (SD), also known as semantic variant primary progressive aphasia (svPPA), is a progressive neurodegenerative disorder characterized by loss of semantic memory in both the verbal and non-verbal domains. However, the most common presenting symptoms are in the verbal domain. Semantic dementia is a disorder of semantic memory that causes patients to lose the ability to match words or images to their meanings. However, it is fairly rare for patients with semantic dementia to develop category specific impairments, though there have been documented cases of it occurring. Typically, a more generalized semantic impairment results from dimmed semantic representations in the brain.
Cerebral amyloid angiopathy (CAA) is a form of angiopathy in which amyloid beta peptide deposits in the walls of small to medium blood vessels of the central nervous system and meninges. The term congophilic is sometimes used because the presence of the abnormal aggregations of amyloid can be demonstrated by microscopic examination of brain tissue after staining with Congo red. The amyloid material is only found in the brain and as such the disease is not related to other forms of amyloidosis.
Primary progressive aphasia (PPA) is a type of neurological syndrome in which language capabilities slowly and progressively become impaired. As with other types of aphasia, the symptoms that accompany PPA depend on what parts of the left hemisphere are significantly damaged. However, unlike most other aphasias, PPA results from continuous deterioration in brain tissue, which leads to early symptoms being far less detrimental than later symptoms.
A perivascular space, also known as a Virchow–Robin space, is a fluid-filled space surrounding certain blood vessels in several organs, including the brain, potentially having an immunological function, but more broadly a dispersive role for neural and blood-derived messengers. The brain pia mater is reflected from the surface of the brain onto the surface of blood vessels in the subarachnoid space. In the brain, perivascular cuffs are regions of leukocyte aggregation in the perivascular spaces, usually found in patients with viral encephalitis.
Corticobasal degeneration (CBD) is a rare neurodegenerative disease involving the cerebral cortex and the basal ganglia. CBD symptoms typically begin in people from 50 to 70 years of age, and the average disease duration is six years. It is characterized by marked disorders in movement and cognition, and is classified as one of the Parkinson plus syndromes. Diagnosis is difficult, as symptoms are often similar to those of other disorders, such as Parkinson's disease, progressive supranuclear palsy, and dementia with Lewy bodies, and a definitive diagnosis of CBD can only be made upon neuropathologic examination.
HIV-associated neurocognitive disorders (HAND) are neurological disorders associated with HIV infection and AIDS. It is a syndrome of progressive deterioration of memory, cognition, behavior, and motor function in HIV-infected individuals during the late stages of the disease, when immunodeficiency is severe. HAND may include neurological disorders of various severity. HIV-associated neurocognitive disorders are associated with a metabolic encephalopathy induced by HIV infection and fueled by immune activation of macrophages and microglia. These cells are actively infected with HIV and secrete neurotoxins of both host and viral origin. The essential features of HIV-associated dementia (HAD) are disabling cognitive impairment accompanied by motor dysfunction, speech problems and behavioral change. Cognitive impairment is characterised by mental slowness, trouble with memory and poor concentration. Motor symptoms include a loss of fine motor control leading to clumsiness, poor balance and tremors. Behavioral changes may include apathy, lethargy and diminished emotional responses and spontaneity. Histopathologically, it is identified by the infiltration of monocytes and macrophages into the central nervous system (CNS), gliosis, pallor of myelin sheaths, abnormalities of dendritic processes and neuronal loss.
Psychoorganic syndrome (POS), also known as organic psychosyndrome, is a progressive disease comparable to presenile dementia. It consists of psychopathological complex of symptoms that are caused by organic brain disorders that involve a reduction in memory and intellect. Psychoorganic syndrome is often accompanied by asthenia.
The inferior temporal gyrus is one of three gyri of the temporal lobe and is located below the middle temporal gyrus, connected behind with the inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface of the temporal lobe, where it is limited by the inferior sulcus. This region is one of the higher levels of the ventral stream of visual processing, associated with the representation of objects, places, faces, and colors. It may also be involved in face perception, and in the recognition of numbers and words.
A neurodegenerative disease is caused by the progressive loss of structure or function of neurons, in the process known as neurodegeneration. Such neuronal damage may ultimately involve cell death. Neurodegenerative diseases include amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease, multiple system atrophy, tauopathies, and prion diseases. Neurodegeneration can be found in the brain at many different levels of neuronal circuitry, ranging from molecular to systemic. Because there is no known way to reverse the progressive degeneration of neurons, these diseases are considered to be incurable; however research has shown that the two major contributing factors to neurodegeneration are oxidative stress and inflammation. Biomedical research has revealed many similarities between these diseases at the subcellular level, including atypical protein assemblies and induced cell death. These similarities suggest that therapeutic advances against one neurodegenerative disease might ameliorate other diseases as well.
Alcohol-related dementia (ARD) is a form of dementia caused by long-term, excessive consumption of alcoholic beverages, resulting in neurological damage and impaired cognitive function.
Posterior cortical atrophy (PCA), also called Benson's syndrome, is a rare form of dementia which is considered a visual variant or an atypical variant of Alzheimer's disease (AD). The disease causes atrophy of the posterior part of the cerebral cortex, resulting in the progressive disruption of complex visual processing. PCA was first described by D. Frank Benson in 1988.
Alzheimer's Disease Neuroimaging Initiative (ADNI) is a multisite study that aims to improve clinical trials for the prevention and treatment of Alzheimer's disease (AD). This cooperative study combines expertise and funding from the private and public sector to study subjects with AD, as well as those who may develop AD and controls with no signs of cognitive impairment. Researchers at 63 sites in the US and Canada track the progression of AD in the human brain with neuroimaging, biochemical, and genetic biological markers. This knowledge helps to find better clinical trials for the prevention and treatment of AD. ADNI has made a global impact, firstly by developing a set of standardized protocols to allow the comparison of results from multiple centers, and secondly by its data-sharing policy which makes available all at the data without embargo to qualified researchers worldwide. To date, over 1000 scientific publications have used ADNI data. A number of other initiatives related to AD and other diseases have been designed and implemented using ADNI as a model. ADNI has been running since 2004 and is currently funded until 2021.
The glymphatic system is a system for waste clearance in the central nervous system (CNS) of vertebrates. According to this model, cerebrospinal fluid (CSF) flows into the paravascular space around cerebral arteries, combining with interstitial fluid (ISF) and parenchymal solutes, and exiting down venous paravascular spaces. The pathway consists of a para-arterial influx route for CSF to enter the brain parenchyma, coupled to a clearance mechanism for the removal of interstitial fluid (ISF) and extracellular solutes from the interstitial compartments of the brain and spinal cord. Exchange of solutes between CSF and ISF is driven primarily by arterial pulsation and regulated during sleep by the expansion and contraction of brain extracellular space. Clearance of soluble proteins, waste products, and excess extracellular fluid is accomplished through convective bulk flow of ISF, facilitated by astrocytic aquaporin 4 (AQP4) water channels.
Alcohol-related brain damage alters both the structure and function of the brain as a result of the direct neurotoxic effects of alcohol intoxication or acute alcohol withdrawal. Increased alcohol intake is associated with damage to brain regions including the frontal lobe, limbic system, and cerebellum, with widespread cerebral atrophy, or brain shrinkage caused by neuron degeneration. This damage can be seen on neuroimaging scans.
The neurovascular unit (NVU) comprises the components of the brain that collectively regulate cerebral blood flow in order to deliver the requisite nutrients to activated neurons. The NVU addresses the brain's unique dilemma of having high energy demands yet low energy storage capacity. In order to function properly, the brain must receive substrates for energy metabolism–mainly glucose–in specific areas, quantities, and times. Neurons do not have the same ability as, for example, muscle cells, which can use up their energy reserves and refill them later; therefore, cerebral metabolism must be driven in the moment. The neurovascular unit facilitates this ad hoc delivery and, thus, ensures that neuronal activity can continue seamlessly.
