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Early Theories of Memory (Ancient Greece - 19th Century)

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Early Theories of Memory (Ancient Greece - 19th Century)

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Aristotle and early philosophers speculated on memory as an abstract process

When: 4th century BCE

Where: Greece

Context: Early ideas viewed memory as an ethereal, spiritual phenomenon rather than a biological process.

Sources: https://www.bloomsbury.com/in/philoponus-on-aristotle-on-the-intellect-de-anima-348-9781780934389/

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First Studies of the Nervous System (1600s-1800s)

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First Studies of the Nervous System (1600s-1800s)

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Santiago Ramón y Cajal’s neuron doctrine

When: 19th century

Where: Spain

Context: Cajal’s research helped establish that the nervous system is composed of individual neurons, laying the groundwork for later studies on synapses.

Sources: https://www.npr.org/sections/health-shots/2017/01/26/511455876/art-exhibition-celebrates-drawings-by-the-founder-of-modern-neuroscience

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Sherrington introduced the concept of synapses as communication points between neurons.

When: 1897

Where: Britain

Context: This research led to the realization that synapses could change over time, an essential component of memory formation.

Sources: https://www.researchgate.net/figure/Sir-Charles-Sherrington-the-first-897-description-of-decerebrate-rigidity_fig10_278047851

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Donald Hebb theorized that "neurons that fire together, wire together."

When: 1949

Where: Canada

Context: This idea became foundational for later research on synaptic strengthening in memory.

Source: https://en.wikipedia.org/wiki/Organization_of_Behavior

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Loewi and Dale demonstrated that neurons communicate via chemical messengers.

When: 1950s

Where: Germany & Britain

Context: The discovery of neurotransmitters was crucial for understanding synaptic changes in learning.

Source: https://www.researchgate.net/figure/Experiment-of-Otto-Loewi_fig4_270552782

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Kandel’s Early Research on Aplysia (1960s)

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Kandel’s Early Research on Aplysia (1960s)

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Kandel studied how simple organisms like Aplysia form memories.

When: 1960s

Where: USA

Context: Kandel’s research showed that memory could be traced to specific biochemical changes in synapses.

Sources:

https://www.inverse.com/mind-body/sea-slug-human-learning-behavior

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Long-Term Potentiation (LTP) Discovery (1973)

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Long-Term Potentiation (LTP) Discovery (1973)

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Scientists discovered that repeated stimulation of a synapse strengthens its response, a key mechanism of memory.

When: 1973

Where: USA

Context: This mechanism aligns with Kandel’s work, showing how memories form through strengthened neural connections.

Sources: https://qbi.uq.edu.au/brain-basics/brain/brain-physiology/long-term-synaptic-plasticity

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Long-term synaptic plasticity was first reported in 1973. Studying a pathway in the rabbit hippocampus, researchers discovered that rapidly and repeatedly activating the synapses made them stronger; the volume control was turned up and stayed that way. They called this long-lasting increase in synaptic strength long-term potentiation, or LTP. The reverse phenomenon, in which synapses become weaker for extended periods, also exists, and is called long-term depression, or LTD.

The strength of synapses can be increased or decreased, and whether or not and in which direction they change depends on their activity patterns. Very active synapses are likely to become stronger (LTP), and those that are less active, or less effective at causing an action potential, tend to become weaker (LTD). Long-term synaptic plasticity forms the model for memory storage.

How do synapses change their strength?

After a neuron fires an action potential, there are three main steps to synaptic transmission:

1. Neurotransmitter release

2. Binding of neurotransmitter to postsynaptic receptors, and

3. Opening of ion channels in the postsynaptic neuron, which allows electrical currents to flow in or out of the cell.

As seen in the diagram below, synaptic plasticity can change either the amount of neurotransmitter released (1) or the number of postsynaptic receptors available (2). Both have the effect of altering how much electrical current flows through the ion channels (3); in other words, these processes change synaptic strength.

Synaptic plasticity can change either the amount of neurotransmitter released (1) or the number of postsynaptic receptors available (2), resulting in changes in synaptic strength. (Image: Alan Woodruff / QBI)

VIDEO: Synaptic plasticity explained

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What is long-term synaptic plasticity and how does it help form new memories?

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Kandel’s Research on Synaptic Strengthening (1980s)

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Kandel’s Research on Synaptic Strengthening (1980s)

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Kandel showed that memory storage involves changes in synaptic strength and gene expression.

When: 1980s

Where: USA

Context: His work demonstrated that learning causes structural changes in neurons.

Sources: https://autism.fratnow.com/blog/brain-plasticity-synapses-dendritic-spines-neural-dynamics/

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Mani T. Valarmathi, M.D. (Pathology), Ph.D. (Biotechnology)

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Brain Plasticity: Synapses, Spines, and Neural Networks | FRAT

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Uncover the brain’s incredible adaptability and lifelong learning. Explore synapses, dendritic spines, the ‘mushrooms of learning,’ and delve into neural plasticity to boost cognitive abilities.

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Application of Kandel’s Research to Human Memory Disorders (1990s)

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Application of Kandel’s Research to Human Memory Disorders (1990s)

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Kandel’s findings were applied to understanding memory loss in Alzheimer’s disease.

When: 1990s

Where: USA

Context: This research helped in developing treatments targeting synaptic function.

Sources: https://www.pacificneuroscienceinstitute.org/brain-health/services/brain-imaging/

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Eric Kandel won the Nobel Prize for his work on learning and memory.

When: 2000

Where: Sweden

Context: His research provided the first direct link between molecular changes and memory formation.

Sources: https://www.meduniwien.ac.at/web/en/about-us/news/detailsite/2019/news-im-november-2019/a-celebration-for-eric-kandel/

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Scientists use optogenetics to activate or suppress specific memories.

When: 2010-2020

Where: USA

Context: Kandel’s foundational work led to cutting-edge techniques like optogenetics, which allows researchers to control memory formation in real-time using light.

Sources/Citations: https://behavioralscientist.org/manipulating-memory-through-optogenetics-qa-with-neuroscientists-xu-liu-and-steve-ramirez/

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Eric Kandel, neuroscientist specializing in memory research. Born in 1929, active research from 1960s-present.

Lifestyle & Experiences:

Born in Vienna, Austria, Kandel fled Nazi persecution as a child and later studied neuroscience in the USA. He was fascinated by how memories form and chose Aplysia as his model organism.

His research demonstrated that synaptic changes underlie learning and memory, influencing treatments for Alzheimer’s and PTSD. He remains active in neuroscience, writing books and engaging in public education.

Source 1: https://www.gettyimages.in/photos/eric-kandel?page=2

Source 2: https://laskerfoundation.org/eric-kandel-learning-about-the-human-brain-from-sea-slugs/