Notes

Why do we need plasticity/learning? The C.Elegans genome stores all synaptic connections. The simple worm C. Elegans, for example, has 302 neurons and about 7000 synapses and in each individual of an inbred strain, the wiring pattern is exactly the same (Chen et al., 2006).

Connections in the human Brain are mostly learned: The human brain has about 10ˆ11 neurons, and more than 10ˆ3 synapses per neuron. Specifying a connection target requires about log_2 10ˆ11 + 35 bits/synapse. Thus, it would take 3.5 x 10ˆ15 bits (approx. 400TB) to specify all 10ˆ14 connections in thebrain. However, the human genome only has about 3 x 10ˆ9 nucleotides, so it cannot encode more than approx. 1GB of information (Wel et al., 2013). Conclusion: Even if every nucleotide of the human genome were devoted to efficiently specifying brain connections, the information capacity is orders of magnitude too small to encode all synaptic connections. Why do we need learning! We need learning to survive and adapt to new situations in a changing environment. Learning as evolutionary survival strategy. Is the brain a Universal Learning Machine? A species using the mixed strategy may thrive if that strategy achieves a higher asymptotic level of performance. Suggested paper: A Critique of Pure Learning: "What Artificial Neural Networks can Learn from Animal Brains" - Zador Intelligent Behaviour Emerges with Learning!

Defining Plasticity/Learning (Learning & Memory vs. Plasticity)

• Learning: The acquisition/storage of knowledge/information or the formation of a memory through experience.
• Memory: Stored information that can be recalled at a later stage in time
  • Learning results in memory - which itself has a further outcome - a change in future behaviour.
  • Learning does not always imply a conscious attempt to learn. Simple observation can lead to the creation of a new memory.
• Plasticity: the biological implementation of learning. Plasticity allows us to form a memory.

Learning in Computer Science

• Machine Learning
  • Supervised Learning (Regression & Classification)
  • Unsupervised Learning (Clustering & Dimensionality Reduction)
  • Reinforcement Learning

Learning in Neuroscience

• Pavlovian Conditioning
• Instrumental Conditioning
• Reward/Aversive Learning
• Social Learning
• Perceptual Learning
• Motor Learning

Network and Systems Plasticity Neural Substrates of Plasticity

How does the brain implement a learning? The Hippocampus as a Model System to Study Learning and Memory

Henry Gustav Molaison (H.M.) 1926 - 20008 Amygdala, hippocampal gyrus, and anterior two third of the hippocampus were removed.

Diagnosis: Severe anterograde amnesia

• Normal STM
• Normal LTM (for events prior to surgery)
• Problem: transfer from STM to LTM
• Could not consolidate new declarative knowledge
• Capable of acquiring implicit knowledge

Conclusions:

• The Hippocampus is not a permanent storage area for explicit knowledge.
• The Hippocampus is involved (with other cortical areas) in consolidation, a longer term process taking months to years (note retrograde amnesia in hippocampus lesion patients for up to 3 years).
• Consolidation is understood to involve biological changes taking place in those other areas of cortex.
• Once this has fully takin place, the hippocampus is not required for retrieval.

Cellular Plasticity, the Perceptron

The Hippocampus and Spatial Memory

Morris Water Maze

How can we measure neuronal plasticity in the Hippocampus?