How the Brain Works The Facts Visually Explained by DK (z-lib.org)

THE PHYSICAL BRAIN

Networks in the Brain

Networks

in the Brain

The patterns of nerve-cell connections in the

human brain are believed to influence how

it processes sensory perceptions, performs

cognitive tasks, and stores memories.

Wiring the brain

The dominant theory of how the brain remembers

and learns can be summed up by the phrase “the

cells that fire together, wire together.” It suggests

that repeated communication between cells creates

stronger connections between them, and a network

of cells emerges in the brain that is associated with

a specific mental process—such as a movement,

a thought, or even a memory (see pp.136–37).

Weak

synapses

KEY

Glutamate

neurotransmitter

Magnesium

ion

Calcium ion

Channel

Glutamate

receptor

Channel blocked

In a weak connection, magnesium ions block

the passage of calcium ions into the dendrite of a

receiving neuron. A glutamate neurotransmitter

received from the axon will open that channel.

1

Neuroplasticity

The networks of the brain are not

fixed but seem to change and adapt

in accordance with mental and

physical processes. This means

that old circuits associated with

one memory or a skill that is no

longer in use fade in strength as

the brain devotes attention to

another and forms a new network

with other cells. Neuroscientists

say the brain is plastic, meaning its

cells and the connections between

them can be reformed many times

over as required. Neuroplasticity

allows brains to recover abilities

lost due to brain damage.

Synaptic weight

Little-used connections

have channels blocked

by magnesium ions. As the

strength of a connection

between two neurons in

a network increases, the

channel is unblocked, and

the number of receptors

at the synapse increases.

BRAIN PATHWAYS

Strong

synapses

Magnesium ion

blocks channel

Calcium unable

to access channel

DENDRITE

SYNAPTIC CLEFT

AXON

Glutamate

neurotransmitter

binds to receptor,

eventually causing

channel to unblock

Axon releases

glutamate

neurotransmitter

Calcium ions

facilitate signaling

between neurons

WHAT IS THE BRAIN’S

DEFAULT MODE NETWORK?

It is a group of brain regions

that show low activity levels

when engaged in a task such

as paying attention but high

activity levels when awake and

not engaged in a specific

mental task.

US_026-027_Networks_in_the_Brain.indd 26 20/09/2019 12:31