Ovoid neurons – a new discovery in neuroscience

Do you remember the first time you saw a molecule of a medicine or, for example, hemoglobin? Probably not – but your brain does. There is a special mechanism for recognizing and storing new information, and it has recently received a new explanation. Scientists at the UBC Faculty of Medicine have discovered a new group of nerve cells – ovoid neurons – that respond only to new information. This discovery has changed how we understand memory and its key stages – especially the moment when the brain decides what to keep and what to discard.

What do we currently know about memory?

Memory is a complex neurocognitive process involving different parts of the brain. There are two main types of memory – explicit and implicit. Explicit memory involves remembering facts, events, and people, and it requires conscious recall. It activates the hippocampus and nearby cortices. On the other hand, implicit memory refers to perceptual and motor skills and does not require conscious effort. It involves the cerebellum, striatum, and amygdala.

The process of forming memory is both interesting and dynamic. It consists of three stages: encoding, storage, and retrieval.

The first step is the formation of short-term memory, which begins with the encoding phase. A stimulus activates a sensory neuron, leading to a temporary increase in cAMP. In response, the sensory neuron releases glutamate into the synaptic cleft, which briefly strengthens the connection between the sensory and motor neurons.

Long-term memory forms when the stimulation – or strengthening of the synaptic connection – lasts from several days to weeks. Constant stimulation of the sensory neuron leads to changes in gene expression and the creation of new proteins. Eventually, the neuron grows, new dendrites form, and new synaptic connections are created. These changes occur not only in sensory neurons but also in motor neurons. This means that learning results in certain anatomical changes, and memory is stored within these structures.

Where do ovoid neurons come in?

The hippocampus – a part of the brain essential for memory and spatial navigation – has been the focus of many studies. It plays a central role in converting short-term memory into long-term memory but does not store it.

The hippocampus is mostly made up of pyramidal neurons, which are responsible for these processes. However, a group of researchers discovered a new type of neuron in the mouse hippocampus – ovoid neurons. These are located near pyramidal neurons but differ in gene expression, shape, electrical activity, and connectivity.

These unique neurons are activated only when encountering a new object. Every later encounter with the same object – even months later – does not activate these excitatory neurons again.

Why is this important?

We have long known that the hippocampus is involved in both spatial and non-spatial learning, but it was unclear whether these were connected or separate processes. The discovery that ovoid neurons react only to new objects, and not to changes in space, suggests that these two processes are indeed separate.

Experiments have shown that these neurons are crucial for the encoding phase, but they do not encode specific details about the object. It is believed that once activated, ovoid neurons send a “broad” signal of novelty that triggers more complex memory systems downstream. These systems then take over and encode the specific information about the new object.

New insights ahead

Like every new discovery, this one opens the door to new ideas and understandings. The discovery of ovoid neurons and their role may help us better understand various neurological disorders, such as epilepsy and Alzheimer’s disease. Experiments show that ovoid neurons are hyperexcitable, which suggests they may play a role in starting and spreading epileptic seizures. As such, they have become targets for new epilepsy treatments. On the other hand, by manipulating these neurons, we might influence memory loss in Alzheimer’s disease.

The discovery of ovoid neurons has opened a whole new chapter in understanding – and potentially treating – the human brain. They offer a new perspective and have fundamentally changed how we view memory. It makes you wonder – how much do we still not know?

Translated by: Josip Kokanović