Embryonic neural development. Notes to supplement lecture notes:

The nervous system starts developing at approximately 15 embryonic days. At this point cells begin to differentiate into mesoderm, endoderm, and ectoderm. The proliferative zone is in the center of the neural tube, and contains one layer of cells. These progenitor cells' nuclei move in a regular way from the center to the edge of the proliferative zone. When each of these returns to the center of the proliferative zone it divides in 2. This process causes the number of progenitor cells to increase very rapidly (exponentially). And the eventual size of the cortex depends on the amount of time the progenitor cells in the proliferative zone have to divide.

Beginning on embryonic day 42, when some progenitor cells divide in the proliferative zone, one of the resulting two cells differentiates into a "primitive neuron." the primitive neurons, thus formed, then leave the proliferative zone and head on their way to their destination in the developing brain.

Idea/Demo: folding, a layered cortex. "areal" structure of cortex.

Idea: additive vs subtractive

Idea: evolutionary age of an ability, and its robustness in the face of injury, ageing, etc.

Idea: neurotrophic factor and number of synapses, and life of neurons.

Idea: ferret experiment, and plasticity of humans seen with deafness/blindness, braille

Picture: the neural plate as seen in a classic anatomy text photograph. Note that Joan Stiles ' pictures from lecture show the neural tube as seen from above, obscuring the rest of the embryo that is below the neural plate.

Stiles 2: early focal lesions, plasticity and subsequent brain development

Language:

In adults, moved and which abilities are in the left hemisphere.

Broca's area: Production of speech. (also note mirror neurons)

Wernicke's area: comprehension.

* of course this is a grossly oversimplified story

Language development:

Early on, language appears to be less localized then later in development:

At 13 months language results in bilateral activity from frontal through parietal lobes,

At 20 months language is left lateralized.

Effect of lesions on children:

Right hemisphere lesions hurt comprehension;

Left posterior lesions hurt production and production of grammar

At age 7, children who had early focal lesions are within the normal range on all language measures;

Between ages 3 and 12, children who had early focal lesions-- though producing perfect speech-- tend to use less complicated grammatical constructions

Spatial cognition:

Adults and children show similar deficits in spatial analysis after injury.

Note: detail (" local features") vs configural (" global") form.

Left posterior injury patients have trouble with details;

Right posterior injury patients have trouble with global form

Some important terms:

Areal structure of cortex. In some ways it makes more sense to think of the brain as a thin sheet that was too big to fit in the skull, and had to be folded quite a bit. Two-dimensional coordinates are usually more useful than three-dimensional coordinates in understanding which parts of cortex have which functions. A lot of research (for instance by Prof. Marty Sereno) has gone into learning how to "Unfold" cortex.

Bilateral. Bilateral tasks use both right and left cerebral hemispheres (sides of the brain), roughly equally.

Commitment. The contribution that sensory input and cells' interactions with each other make to cellular development. " Nurture ." contrasted with lineage.

Frontal lobes. The front portions of the cortex (brain).

Glial cells. These cells are usually thought of as kind of " helper cells" in the nervous system, and in neural development. They produce myelin, which wraps around neurons with longer-distance connections in cortex. Myelin functions like an insulator on electric wire, speeding the transmission of the signal and mitigating the signal's loss of strength. "Radial glial cells" act as a kind of scaffolding to help primitive neurons move from the proliferative zone to their destinations in cortex, in embryonic neural development.

Laminar. Having a layered structure. Human cortex is laminar, in the sense that different depths of the cortex have different cellular anatomy and function. Like a layer cake.

Lateralized. Tasks that are lateralized make greater (or exclusive) use of one hemisphere. In most adults, language is lateralized in the left hemisphere.

Lexicon. The words of a language. In the context of language development, this refers to the words that a child knows.

Lineage. The contribution that genes make to cellular development. "Nature." "Protomap." contrasted with commitment.

Mesoderm vs. endoderm forces ectoderm. See lecture notes for details. Note that a subset of ectodermal cells, located along the midline of the embryonic neural tube, become neurons, and after receiving a neurolizing signal from mesodermal cells.

Morphology (morphological) (morphosyntax). The formal structure of a language, especially rules for how words are formed (beginnings and endings, verb conjugations).

Occipital lobes. The part of the brain in the back of the head, below the parietal lobes.

Omnipotent stem cells. Note that prior to embryonic day 15, there is no apparent differentiation of embryonic cells. The cells are "omnipotent" in the sense that they could potentially differentiate to later become any kind of cell in the developing fetus and baby.

Ontogeny. An individual's development. Contrasts with phylogeny.

Parietal lobes. The part of the brain behind the frontal lobes, above the temporal lobes, and in front of or above the occipital lobes.

Phylogeny. Evolutionary history.

Process. In the context of neurons, " process" refers to axons and dendrites, the parts of the neurons that extend to help it connect with other neurons.

Temporal lobes. The areas of the cortex behind the frontal lobes, below the parietal lobes, and in front of the occipital lobes. The part of cortex nearest the ears is in the temporal lobes.

Images for Stiles' lectures: regions of cortex

laminar structure of cortex

developing pre-natal nervous system

dorsal vs ventral, etc., explained

Brain development handout, by Laura Kemmer

Preferential looking handout

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