In neuroscience, synaptic plasticity is the ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity. Plastic change also results from the alteration of the number of neurotransmitter receptors located on a synapse. There are several underlying mechanisms that cooperate to achieve synaptic plasticity, including changes in the quantity of neurotransmitters released into a synapse and changes in how effectively cells respond to those neurotransmitters. Synaptic plasticity in both excitatory and inhibitory synapses has been found to be dependent upon postsynaptic calcium release. Since memories are postulated to be represented by vastly interconnected networks of synapses in the brain, synaptic plasticity is one of the important neurochemical foundations of learning and memory (see Hebbian theory). Historical discoveries Synaptic plasticity
Anterograde amnesia Anterograde amnesia is a loss of the ability to create new memories after the event that caused the amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. This is in contrast to retrograde amnesia, where most memories created prior to the event are lost while new memories can still be created. Both can occur together in the same patient. To a large degree, anterograde amnesia remains a mysterious ailment because the precise mechanism of storing memories is not yet well understood, although it is known that the regions involved are certain sites in the temporal cortex, especially in the hippocampus and nearby subcortical regions. Causes
Idiopathic intracranial hypertension Idiopathic intracranial hypertension (IIH), sometimes called by the older names benign intracranial hypertension (BIH) or pseudotumor cerebri (PTC), is a neurological disorder that is characterized by increased intracranial pressure (pressure around the brain) in the absence of a tumor or other diseases. The main symptoms are headache, nausea, and vomiting, as well as pulsatile tinnitus (sounds perceived in the ears, with the sound occurring in the same rhythm as the pulse), double vision and other visual symptoms. If untreated, it may lead to swelling of the optic disc in the eye, which can progress to vision loss. IIH is diagnosed with a brain scan (to rule out other causes) and a lumbar puncture; lumbar puncture may also provide temporary and sometimes permanent relief from the symptoms. Some respond to medication (with the drug acetazolamide), but others require surgery to relieve the pressure.
Cerebral venous sinus thrombosis (CVST) is the presence of thrombosis (a blood clot) in the dural venous sinuses, which drain blood from the brain. Symptoms may include headache, abnormal vision, any of the symptoms of stroke such as weakness of the face and limbs on one side of the body, and seizures. The diagnosis is usually by computed tomography (CT/CAT scan) or magnetic resonance imaging (MRI) employing radiocontrast to demonstrate obstruction of the venous sinuses by thrombus. Treatment is with anticoagulants (medication that suppresses blood clotting), and rarely thrombolysis (enzymatic destruction of the blood clot). Given that there is usually an underlying cause for the disease, tests may be performed to look for these. Cerebral venous sinus thrombosis
Papilledema (or papilloedema) is optic disc swelling that is caused by increased intracranial pressure. The swelling is usually bilateral and can occur over a period of hours to weeks. Unilateral presentation is extremely rare. Papilledema
Deep brain stimulation (DBS) is a surgical treatment involving the implantation of a medical device called a brain pacemaker, which sends electrical impulses to specific parts of the brain. DBS in select brain regions has provided therapeutic benefits for otherwise-treatment-resistant movement and affective disorders such as Parkinson's disease, essential tremor, dystonia, and chronic pain. Despite the long history of DBS, its underlying principles and mechanisms are still not clear. DBS directly changes brain activity in a controlled manner, its effects are reversible (unlike those of lesioning techniques), and it is one of only a few neurosurgical methods that allow blinded studies. Deep brain stimulation
Vagus nerve stimulation Vagus nerve stimulation (VNS) is an adjunctive treatment for certain types of intractable epilepsy and treatment-resistant depression. Mechanism of action Vagus, the tenth cranial nerve, arises from the medulla and carries both afferent and efferent fibers. The afferent vagal fibers connect to the nucleus of the solitary tract which in turn projects connections to other locations in the central nervous system. Little is understood about exactly how vagal nerve stimulation modulates mood and seizure control but proposed mechanisms include alteration of norepinephrine release by projections of solitary tract to the locus coeruleus, elevated levels of inhibitory GABA related to vagal stimulation and inhibition of aberrant cortical activity by reticular system activation.
Temporal lobe epilepsy Introduction Over forty types of epilepsy are recognised and they are divided into two main categories: Partial seizures and generalized seizures. Partial seizures account for approximately sixty percent of all adult cases. Temporal lobe epilepsy (TLE) is the single most common form of partial seizure. Signs and symptoms When a seizure begins in the temporal lobe, the symptoms experienced by the patient, and the signs seen by bystanders, depend on the precise location of the seizure focus. In 1981, the ILAE recognized three types of seizures occurring in temporal lobe epilepsy.
The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet that in medicine is used primarily to treat difficult-to-control (refractory) epilepsy in children. The diet forces the body to burn fats rather than carbohydrates. Normally, the carbohydrates contained in food are converted into glucose, which is then transported around the body and is particularly important in fuelling brain function. However, if there is very little carbohydrate in the diet, the liver converts fat into fatty acids and ketone bodies.
Anatomy The raphe nuclei are traditionally considered to be the medial portion of the reticular formation, and they appear as a ridge of cells in the center and most medial portion of the brain stem. Nomenclature The Latin names commonly used for most of these nuclei are grammatically incorrect. Latin grammar would require nucleus raphe magnus to be changed to nucleus raphes magnus, for example. Terminologia Anatomica, the main authority on anatomical names, uses the "raphes" form, and so do some scientific papers, but in recent years more than 95% of scientific publications have continued to use the "raphe" form, as this article does. Raphe nuclei
MRI coronal view of a hippocampus shown in red The hippocampus (named after its resemblance to the seahorse, from the Greek hippos meaning "horse" and kampos meaning "sea monster") is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is located under the cerebral cortex; and in primates it is located in the medial temporal lobe, underneath the cortical surface. Hippocampus
Declarative memory Declarative memory (sometimes referred to as explicit memory) is one of two types of long-term human memory. Declarative memory refers to memories which can be consciously recalled such as facts and knowledge. Declarative memory's counterpart is known as non-declarative or procedural memory, which refers to unconscious memories such as skills (e.g. learning to ride a bicycle). Declarative memory can be divided into two categories: episodic memory, which stores specific personal experiences, and semantic memory, which stores factual information. Types There are two types of declarative memory: semantic memory and episodic memory.
The suprachiasmatic nucleus or nuclei, abbreviated SCN, is a tiny region located in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms. The neuronal and hormonal activities it generates regulate many different body functions in a 24-hour cycle, using around 20,000 neurons. According to a study conducted on rats, the SCN tends to diminish in size with age. The SCN, which is pine cone-shaped and the size of a grain of rice, interacts with many other regions of the brain. Suprachiasmatic nucleus
Dorsal raphe nucleus The dorsal raphe nucleus is located on the midline of the brainstem and is part of the raphe nucleus, consisting of the rostral and caudal subdivisions. The rostral aspect of the dorsal raphe is further divided into interfascicular, ventral, ventrolateral and dorsal subnuclei.The projections of the dorsal raphe have been found to vary topographically, and thus the subnuclei differ in their projections. An increased number of cells in the lateral aspects of the dorsal raphe is characteristic of humans and other primates.
The locus coeruleus is the principal site for brain synthesis of norepinephrine (noradrenaline). The locus coeruleus and the areas of the body affected by the norepinephrine it produces are described collectively as the locus coeruleus-noradrenergic system or LC-NA system. Norepinephrine may also be released directly into the blood from the adrenal medulla. Name Locus coeruleus
Paraventricular nucleus of hypothalamus
Brodmann area 25