| Day | Event | Reference |
|---|---|---|
| 33 | posterior commissure appears | Ashwell et al. (1996) [2] |
| 33 | medial forebrain bundle appears | Ashwell et al. (1996) [2] |
| 44 | mammillothalamic tract appears | Ashwell et al. (1996) [2] |
| 44 | stria medullaris thalami appears | Ashwell et al. (1996) [2] |
| 51 | axons in optic stalk | Dunlop et al. (1997) [3] |
| 56 | external capsule appears | Ashwell et al. (1996) [2] |
| 56 | stria terminalis appears | Ashwell et al. (1996) [2] |
| 60 | optic axons invade visual centers | Dunlop et al. (1997) [3] |
| 63 | internal capsule appears | Ashwell et al. (1996) [2] |
| 63 | fornix appears | Ashwell et al. (1996) [2] |
| 70 | anterior commissure appears | Ashwell et al. (1996) [2] |
| 77 | hippocampal commissure appears | Ashwell et al. (1996) [2] |
| 87.5 | corpus callosum appears | Ashwell et al. (1996) [2] |
| 157.5 | eye opening | Clancy et al. (2007) [4] |
| 175 | ipsi/contra segregation in LGN and SC | Robinson & Dreher (1990) [5] |
Studies report that three primary structures are formed in the sixth gestational week. These are the forebrain, the midbrain, and the hindbrain, also known as the prosencephalon, mesencephalon, and the rhombencephalon respectively. Five secondary structures originate from these in the seventh gestational week. These are the telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon; the lateral ventricles, third ventricles, cerebral aqueduct, and upper and lower parts of the fourth ventricle in adulthood originated from these structures. [6] The appearance of cortical folds first takes place during 24 and 32 weeks of gestation. [7]
Cortical white matter increases from childhood (~9 years) to adolescence (~14 years), most notably in the frontal and parietal cortices. [8] Cortical grey matter development peaks at ~12 years of age in the frontal and parietal cortices, and 14–16 years in the temporal lobes (with the superior temporal cortex being last to mature), peaking at about roughly the same age in both sexes according to reliable data. In terms of grey matter loss, the sensory and motor regions mature first, followed by other cortical regions. [8] Though it is a controversial psychometric, adult IQ also begins to be tested around this age range, with the Raven's Progressive Matrices test beginning at age 14 and the Wechsler Adult Intelligence Scale test beginning at age 16, though scores between 14 and 16 on the Weschler test have differences so small that they are considered unreliable. This may bring into question the effectiveness of brain development studies in treating and successfully rehabilitating criminal youth. [9]
In the 2010s and beyond, science has shown that the brain continues to develop until at least 30 years of age. [10]
The central nervous system (CNS) is the part of the nervous system consisting of the brain and spinal cord, the retina and optic nerve, and the olfactory nerve and epithelia. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric and triploblastic animals—that is, all multicellular animals except sponges and diploblasts. It is a structure composed of nervous tissue positioned along the rostral to caudal axis of the body and may have an enlarged section at the rostral end which is a brain. Only arthropods, cephalopods and vertebrates have a true brain, though precursor structures exist in onychophorans, gastropods and lancelets.
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.
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. It is the largest site of neural integration in the central nervous system, and plays a key role in attention, perception, awareness, thought, memory, language, and consciousness. The cerebral cortex is the part of the brain responsible for cognition.
Holoprosencephaly (HPE) is a cephalic disorder in which the prosencephalon fails to develop into two hemispheres, typically occurring between the 18th and 28th day of gestation. Normally, the forebrain is formed and the face begins to develop in the fifth and sixth weeks of human pregnancy. The condition also occurs in other species.
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.
The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex, as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In the human brain, the cerebrum is the uppermost region of the central nervous system. The cerebrum develops prenatally from the forebrain (prosencephalon). In mammals, the dorsal telencephalon, or pallium, develops into the cerebral cortex, and the ventral telencephalon, or subpallium, becomes the basal ganglia. The cerebrum is also divided into approximately symmetric left and right cerebral hemispheres.
The brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the body, processing, integrating, and coordinating the information it receives from the sense organs, and making decisions as to the instructions sent to the rest of the body. The brain is contained in, and protected by, the skull bones of the head.
The claustrum is a thin sheet of neurons and supporting glial cells, that connects to the cerebral cortex and subcortical regions including the amygdala, hippocampus and thalamus of the brain. It is located between the insular cortex laterally and the putamen medially, encased by the extreme and external capsules respectively. Blood to the claustrum is supplied by the middle cerebral artery. It is considered to be the most densely connected structure in the brain, and thus hypothesized to allow for the integration of various cortical inputs such as vision, sound and touch, into one experience. Other hypotheses suggest that the claustrum plays a role in salience processing, to direct attention towards the most behaviorally relevant stimuli amongst the background noise. The claustrum is difficult to study given the limited number of individuals with claustral lesions and the poor resolution of neuroimaging.
In the human brain, the diencephalon is a division of the forebrain. It is situated between the telencephalon and the midbrain. The diencephalon has also been known as the tweenbrain in older literature. It consists of structures that are on either side of the third ventricle, including the thalamus, the hypothalamus, the epithalamus and the subthalamus.
Neuroscience and intelligence refers to the various neurological factors that are partly responsible for the variation of intelligence within species or between different species. A large amount of research in this area has been focused on the neural basis of human intelligence. Historic approaches to studying the neuroscience of intelligence consisted of correlating external head parameters, for example head circumference, to intelligence. Post-mortem measures of brain weight and brain volume have also been used. More recent methodologies focus on examining correlates of intelligence within the living brain using techniques such as magnetic resonance imaging (MRI), functional MRI (fMRI), electroencephalography (EEG), positron emission tomography and other non-invasive measures of brain structure and activity.
In psycholinguistics, language processing refers to the way humans use words to communicate ideas and feelings, and how such communications are processed and understood. Language processing is considered to be a uniquely human ability that is not produced with the same grammatical understanding or systematicity in even human's closest primate relatives.
The superior parietal lobule is bounded in front by the upper part of the postcentral sulcus, but is usually connected with the postcentral gyrus above the end of the sulcus. The superior parietal lobule contains Brodmann's areas 5 and 7.
FreeSurfer is brain imaging software originally developed by Bruce Fischl, Anders Dale, Martin Sereno, and Doug Greve. Development and maintenance of FreeSurfer is now the primary responsibility of the Laboratory for Computational Neuroimaging at the Athinoula A. Martinos Center for Biomedical Imaging. FreeSurfer contains a set of programs with a common focus of analyzing magnetic resonance imaging (MRI) scans of brain tissue. It is an important tool in functional brain mapping and contains tools to conduct both volume based and surface based analysis. FreeSurfer includes tools for the reconstruction of topologically correct and geometrically accurate models of both the gray/white and pial surfaces, for measuring cortical thickness, surface area and folding, and for computing inter-subject registration based on the pattern of cortical folds.
The development of the nervous system in humans, or neural development, or neurodevelopment involves the studies of embryology, developmental biology, and neuroscience. These describe the cellular and molecular mechanisms by which the complex nervous system forms in humans, develops during prenatal development, and continues to develop postnatally.
A connectome is a comprehensive map of neural connections in the brain, and may be thought of as its "wiring diagram". An organism's nervous system is made up of neurons which communicate through synapses. A connectome is constructed by tracing the neuron in a nervous system and mapping where neurons are connected through synapses.
In human neuroanatomy, brain asymmetry can refer to at least two quite distinct findings:
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.
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.
The neuroscience of sex differences is the study of characteristics that separate brains of different sexes. Psychological sex differences are thought by some to reflect the interaction of genes, hormones, and social learning on brain development throughout the lifespan. A 2021 meta-synthesis led by Lise Eliot found that sex accounted for 1% of the brain's structure or laterality, finding large group-level differences only in total brain volume. A subsequent 2021 led by Camille Michèle Williams contradicted Eliot's conclusions, finding that sex differences in total brain volume are not accounted for merely by sex differences in height and weight, and that once global brain size is taken into account, there remain numerous regional sex differences in both directions. A 2022 follow-up meta-analysis led by Alex DeCasien analyzed the studies from both Eliot and Williams, concluding that "The human brain shows highly reproducible sex differences in regional brain anatomy above and beyond sex differences in overall brain size" and that these differences are of a "small-moderate effect size." A review from 2006 and a meta-analysis from 2014 found that some evidence from brain morphology and function studies indicates that male and female brains cannot always be assumed to be identical from either a structural or functional perspective, and some brain structures are sexually dimorphic.
The parieto-frontal integration theory (P-FIT) considers intelligence to relate to how well different brain regions integrate to form intelligent behaviors. The theory proposes that large scale brain networks connect brain regions, including regions within frontal, parietal, temporal, and cingulate cortices, underlie the biological basis of human intelligence. These regions, which overlap significantly with the task-positive network, allow the brain to communicate and exchange information efficiently with one another. Support for this theory is primarily based on neuroimaging evidence, with support from lesion studies. The P-FIT is influential in that it explains the majority of current neuroimaging findings, as well as increasing empirical support for cognition being the result of large-scale brain networks, rather than numerous domain-specific processes or modules. A 2010 review of the neuroscience of intelligence described P-FIT as "the best available answer to the question of where in the brain intelligence resides".