THE ORGANIZATION OF BEHAVIOR

…is summarized by the phrase above. Also known as the Cell Assembly theory, this model was introduced by Donald Hebb in the book titled The Organization of Behavior. This fundamental principle,

“Neurons that fire together, wire together; and neurons out of sync, fail to link,”

is a simple and elegant framework to contextualize Associative Learning and understand Neuroplasticity - the brain’s capacity for Re-Organization.

Zooming in to the brain…

…we can find the basic unit of our nervous system - the Neuron.

When neurons “fire,” they communicate with other connected neurons:

Information, in the form of electricity, is transmitted downstream along connected neurons. The scientific term for this kind of “firing electricity” is known as an Action Potential.

The place where a neuron connects with another neuron is called a Synapse:

At the Synapse, this electricity is converted into chemical energy, and information is passed along through molecules known as Neurotransmitters (triangles above).

When Neurotransmitters traverse the Synapse across the synaptic cleft, they bind to the Post-Synaptic Neuron:

Here, the chemical energy is converted back into electricity, causing the Post-Synaptic Neuron to fire.

And because each neuron branches off to connect with numerous other neurons…

…information is distributed throughout the brain in this manner…

…on the order of milliseconds.

Continuously.

Neuroplasticity in Motion:

Left: As the neurons fire, they wire together to strengthen the Synapse.

Right: As the neurons fall out of sync, the Synapse weakens and un-links.

Learning and Memory

As information is distributed along neurons connected within Neural Networks, it is stored in the form of Engrams.

The more the neurons fire, the more potently they wire to integrate the data being processed.

Synaptic strength of the Post-synaptic neuron (green) is much greater after Repeated Stimulation for 1 week. This is measured not only through the synaptic receptor density of the neuron, but also through recordings of a stronger neuronal impulse.

Repeated Stimulation mentioned above includes the kind of stimulation conducted through TMS:

Electrical stimulation vis-à-vis Magnetic stimulation.

How does this increase the synaptic strength?

The answer is Long Term Potentiation:

Long-Term Potentiaion (LTP) describes the long-lasting persistent strengthening of synapses brought about by repeated stimulation.

For reference, Long-Term Depression (LTD) is the opposite of this process. It entails the un-linking of neurons after falling out of sync.

Key Takeaways:

REPEATED NEURONAL STIMULATION (TMS)

↓

GREATER SYNAPTIC STRENGTH

↓

ROBUST LEARNING

↓

DEEPER CONSOLIDATION OF BEHAVIOR INTO MEMORY

Zooming out…

…we can see how changes at the Micro level (Neurons) would influence pathways and connections at the Macro level (Connectome).

The Connectome - the neural connections in our brains - was mapped by the Human Connectome Project (similar to the mapping of our genes in the Human Genome Project):

These neural connections give rise to what are known as Structural and Functional Brain Networks. And as we’ve explored here, these networks can be reconfigured by leveraging Neuroplasticity.