Hebbs Theory

Hebb's theory of learning and neuronal growth

Donald Hebb's theory focuses on the biological consequences of learning and memory. The central idea of Hebb's theory is that the process of learning, which involves a repeated co-activation of neurons, results in the strengthening of the connections between neurons and allows them to communicate more efficiently.

In short, neurons that fire together, wire together. This manifests in our ability to quickly recall information that we revised or perform actions without much effort after a period of practice.

Hebb's theory definition

Hebb's theory proposes a neural mechanism for learning and memory. According to Hebb, as one neuron repeatedly excites another neuron, a synaptic knob grows at the end of its axon to improve the efficiency of transmission. Memories can be represented by a co-activation of a group of neurons.

This group is called a cell assembly. Repeated activation of a cell assembly strengthens connections between the cells forming a neural pathway. Neural pathways are long-lasting and hold representations of our memories and the things we learn.

Aim of Hebb's theory of learning

The aim of Hebb's theory was to provide a biological basis for the formation of new memories, development of skills and memory storage. His theory attempts to explain how repetition impacts neural processes associated with memory consolidation and storage.

Hebb's theory explained

Let's look in detail at the neural mechanisms for learning proposed by Hebb.

The structure of neurons

To better understand how the connections between neurons are made we need to examine the structure of neurons. Neurones consist of a cell body (soma), an axon and dendrites.

Dendrites branch out of the cell body and receive information from other neurons. Axons are long cable-like structures that transmit signals from the neuron to other neurons. Two neurons can communicate through the synapse, a gap between an axon of one neuron and a dendrite of another.

The transmission in the synapse occurs through the release of neurotransmitters into the synapse. As axons and dendrites grow they can create synapses with other neurons.

Formation of neural pathways

The strengthening of connections between neurons can be compared to the growth of muscles, the more a muscle is used the more it strengthens and grows. Stronger muscles allow us to perform certain activities more efficiently.

Similarly, with repeated co-activation, the connections between neurons become stronger and the transmission of information between them more efficient. This strengthening of the connection between neurons was proposed to occur through neural growth, the growth of the synaptic knob at the end of the axon.

As more neurons wire together, cell assemblies are created. Cell assemblies involve groups of neurons that will co-activate in response to a stimulus. The co-activation of a cell assembly creates a temporary trace in the brain that represents a memory. This cell assembly representing a unit of memory can be referred to as an engram.

Cell assemblies can be strengthened through repeated activation, forming a neural pathway, a group of interconnected cells, activation of which represents information stored in long-term memory.

Brain plasticity

Hebb's theory supports the notion of brain plasticity.

Brain plasticity involves two main processes:

• Neural growth and neural pruning

The pathways and neurons that are frequently used are strengthened, while the pathways that are not used are gradually pruned or eliminated. In the adult brain, new neurons are generated mainly in the hippocampus, which is the area responsible for learning and memory.

Hebb's theory psychology: Evaluation

Hebb's theory continues to be influential as it produces testable hypotheses that have been supported by behavioural and neuroscientific research. A range of practical applications can also be attributed to the theory. However, the theory has been criticised for reductionism.

Supporting evidence

• Bliss and Lomo (1973) investigated the effects of repeated co-activation of neurons in the hippocampi of rabbits. They found that repeated stimulation of the receiving neuron by another neuron resulted in changes in its activity. The activity of the receiving neuron became faster, greater and more long-lasting. It was concluded that repeated co-activation makes the transmission between neurons more efficient.

• Maguire et al. (2000) conducted brain scans of London taxi drivers. It was found that the size of the hippocampus in taxi drivers was larger than in healthy controls. Moreover, the size of the hippocampus was found to correlate with the time they have been taxi drivers. This study indicates that experience, in this case learning how to navigate the streets of London, has the ability to affect our brain structure.

• Memory research - Hebb proposed an experimental paradigm to investigate the role of repetition in learning. Participants were asked to immediately recall sequences of numbers. Every third sequence they were presented was identical, they were exposed to it repeatedly which allowed them to practice. It was found that participants were able to improve their accuracy in recalling the repeated sequence while their ability to recall other sequences, presented only once, didn't improve.

Applications

• Since experiences can lead to the growth of new neurons and the formation of neural pathways, the Hebbian theory suggests that stimulating environments that provide children with opportunities for a lot of new experiences are beneficial for their neural development.
• Similarly, promoting the formation of new neurons through continuous learning and new experiences could be a protective factor from neurodegenerative diseases like dementia.
• The concept of brain plasticity can explain recovery from stroke or traumatic brain injury, which can result in the death of neurons in some parts of the brain. Due to the brain's capacity to rewire itself, it is possible for stroke and traumatic brain injury patients to regain some of the lost functions with rehabilitation.

Reductionism

One criticism of the theory is that is reductionist. Hebb reduces a complex phenomenon of learning to the firing of neurons. Hebb's theory can be also contrasted with other theories putting an emphasis on social and cognitive aspects of learning like Piaget's theory of cognitive development or Vygotsky's sociocultural theory of development.