Neurocognition Lecture 1 | Development: The brain and cognition over the life span
Part 1: Brain structure & anatomy – refresher
- Neurons and other cells in the nervous system
Parts you should be
able to identify: Cell
body, Axon, Axon
hillock, Dendrites,
Synapse/synaptic cleft
(pre- and post &
vesicles and receptors),
Myelin sheath (nodes
of Ranvier)
*Neurons: can be wildly different in terms of their shape and function
- Sensory → afferent = towards the brain
- Interneurons → stellate, pyramidal, purkinje
- Motor → efferent = away from the brain
*Action potentials: thresholded, non-decremental, all-or-nothing response. Triggered by
summation of excitatory potentials. Driven by varying ion permeability of cell membrane. Propagates
along axon, can travel for a meter or more. Triggers neurotransmitter release at axon terminal
*Synapse: Action potentials leads to neurotransmitter release into synaptic cleft:
- Some neurons can release more than one type of neurotransmitter, depending on
type of stimulation (e.g. low vs. high frequency stimulation)
*Acetylcholine, dopamine, norepinephrine, serotonin, glutamate, GABA
- Receptor cells in the postsynaptic membrane can adapt to under- or over-use
- The distribution of synapses connecting to a cell influences its excitability
*Glia cells: also in different shapes and functions
- Astrocytes: blood-brain barrier, structural support
- Oligodendrocytes: Myelin for CNS neurons
- Microglial cells: fight infections, waste disposal
- Ependymal cells: ventricular surface epithelium, create CSF
- Schwann cells: myelin for peripheral neurons
*Cortical cell layers:
- Different types of neuron are often organized in layers
- Sensory (input), interneurons (relay), and motor (output) neurons are grouped
- Layers are different in different cortical areas, depending on primary function. So a
brain area that is mostly focused on perception will likely have a thicker layer for input neurons than
it does for output neurons
- Each layer has a specific function:
, *White matter tracts: bundles of myelinated axons
- Connecting neurons throughout the central and peripheral nervous system
*Association fibers connecting areas within a hemisphere
*Commissural fibers crossing to the other hemisphere, to the same
(homotopic) or a different place (heterotopic)
*Projection fibers connect outward, to subcortical regions, cerebellum or the
spinal chord
- White matter tracts can indicate how well areas are connected
*Major components of the CNS:
- Forebrain, incl. hemisphere, corpus callosum, and subcortical deep structure
(telencephalon). Is bigger in humans. Subcortical: technically anything below/surrounded by the
cortex
*Basal ganglia:
- Caudate nucleus, Putamen, Globus pallidus (all 3 really deep in the
brain)
- Subthalamic nucleus (STN)
- Substantia nigra
- Basal ganglia circuits: multiple circuits in the brain go through the
basal ganglia
*Motor circuit: organizing voluntary movement through
inhibitory and excitatory pathways
*Associative circuit: contributing to leaning, predictive
processing, sequencing
*Reward circuit: producing pleasure responses, motivational
functions
*Limbic structures: most important for stress response and emotions
- Cingulate (part of cortex!)
- Hippocampus, hypothalamus, amygdala
*Telencephalon contains also cortical structures. Cortical lobes:
- Frontal lobes: movement, attention, reward, short-term memory,
planning, impulse control, and more
- Parietal lobes: sensory integration, association processes, language
functions, spatial processing, sense of touch, some visual processes, and more
- Occipital lobes: mainly primary visual areas
- Temporal lobes: memory, emotion association, primary auditory
areas, some visual processes, and more!
, - Diencephalon, incl. thalamic structures:
*Thalamus, hypothalamus, pituary gland
*Thalamus is an important relay station → every information that goes in or
out passes through the thalamus at some point. It delivers signals to almost the whole brain. Damage
can have wildly scoped consequences.
- Midbrain (mesencephalon), top of brain stem, incl. sensory and motor relay nuclei:
*Superior/inferior colliculi: contribute to sensory processing
*Substantia nigra: contributes to movement initiation
*Origin of cranial nerves II-IV
- Hindbrain (metencephalon):
*Medulla oblongata: contributes to vital reflexes, damage is often fatal
*Pons: crossing over of many fibers in the motor and sensory pathways for
contralateral motor control
*Cerebellum: automated movements, balance, timing & time perception,
sensorimotor coupling, attention shifting, other cognitive functions
*Origin of cranial nerves V-XII
- Spinal chord
*Lateralization: symmetry and asymmetry
- Many functions are the same across inter-hemispheric homologues
*Primary perception areas with cross-lateralized fields: vision, touch
*Sensory and motor homunculus
*Auditory perception is partly bilateral
- Functional asymmetries:
*Language usually left-lateralized (not for everyone, but for right handed
people definitely), nonverbal material on the right
*Global perception is usually right-lateralized, local perception is on the left
*Creative vs logical contrast does not hold, most functions need both
hemispheres to be performed correctly
- Split brain studies
*The wrinkled surface of the cortex is described in terms of:
- Gyri (gyrus) = bump or ridge in the wrinkles
- Sulci (sulcus) = groove in the wrinkles, some are also called fissures (big/deep
sulcus)
- Fissures, sulci & gyri are recognizable landmarks in the brain
*Ventricles of the brain are the open spaces in the brain where CSF is circulating
- CSF runs through the ventricles, subarachnoid space and venous sinus and is created
in the lateral ventricles from arterial blood in the choroid plexus and ependymal cells. The function of
this fluid is to cushion and protect the brain.
*Meninges: multiple membranes covering the brain and spinal chord (from outside): dura
mater (outer and inner layers), arachnoid with subarachnoid space, pia mater
Naming conventions:
- Multiple ways of finding your way in the brain:
*Brodmann Areas: histological!
- Only sometimes overlap with functionally distinct areas
*Functional names, e.g. ‘primary motor cortex’
- Exact location can stay vague, assumes one function per area (!)
, *Relative locations, e.g. dorsolateral frontal cortex, ventromedial thalamic nucleus
- Need to know the directional planes
*Coordinate systems, e.g. values for x-, y- and z-axes
- Most exact, but multiple coordinate systems exist (!)
- Getting oriented in the brain: x, y and z coordinates
*Talairach coordinates (based on one elderly lady’s brain)
*MNI coordinates (based on ‘standard brain’: avg of 152 brains)
- Many atlases exist to map coordinates to functional areas!
- dorsal = back & ventral = belly
Halfway summary:
- There are various kinds of neural and glial cells that are classified based on their shape, location and
function
- Neurons communicate through action potentials and synaptic transfer
- Grey matter consists of neuronal cell bodies and glia cells, situated on the outer layer of the
hemispheres (cortex) and in subcortical nuclei
- White matter consists of neuronal axons and glia cells, organized in bundles that connects different
grey matter areas
- Major components can be identified (e.g. hindbrain, midbrain etc) and subdivided into specific areas
(e.g. pons, thalamus, etc etc etc)
- Some areas are highly specialized, and some are not, some only have relay/gating functions.
- Brain areas are not necessarily mapped one-to-one with specific functions
- Although many brain areas have homologues in each hemisphere, some areas do not
- The brain floats in CSF, which circulates through the ventricles and around the brain under the
meninges
- There are multiple ways to name a location in the brain: Relative (dimensional), exact (coordinates),
or functional
Part 2: Brain development and plasticity
Standard brain templates exist, but it’s important to know that this standard brain does not exist.
Everyone deviates from the templates. Standard brain allows finding comparable locations between
individuals.
- Warping an individual brain to match the template
Behavioral correlates of structural differences:
- Often structural differences between individual brains mean very little. However, sometimes
we can relate structural differences to cognitive deficits. Also cortical thickness (grey matter layer)
