Why do some neurons respond so selectively to words, objects and faces?

Why do some neurons respond so selectively to words, objects and faces?

Some neurons in the brain respond to words, objects and faces in a highly selective manner, consistent with the so-called 'grandmother cell' theory whereby a particular neuron activates when a person sees, hears or otherwise senses a specific entity, such as his or her grandmother. For example, a neuron in a human was found to respond to images of Jennifer Aniston but not to other people, objects or scenes.

So why do neurons respond in this remarkable way? A new study by Professor Jeff Bowers and colleagues at the University of Bristol argues that highly selective are well suited to co-activating multiple things, such as words, objects and faces, at the same time in short-term memory.

The researchers trained an to remember words in short-term memory. Like a brain, the network was composed of a set of interconnected units that activated in response to inputs; the network 'learnt' by changing the strength of connections between units. The researchers then recorded the activation of the units in response to a number of different words.

When the network was trained to store one word at a time in short-term memory, it learned highly distributed codes such that each unit responded to many different words. However, when it was trained to store multiple words at the same time in short-term memory it learned highly selective ('grandmother cell') units – that is, after training, single units responded to one word but not any other. This is much like the neurons in the cortex that respond to one face amongst many.

Why did the network learn such highly specific representations when trained to co-activate multiple words at the same time? Professor Bowers and colleagues argue that the non-selective representations can support memory for a single word, given that a pattern of activation across many non-selective units can uniquely represent a specific word. However, when multiple patterns are mixed together, the resulting blend pattern is often ambiguous (the so-called 'superposition catastrophe').

This ambiguity is easily avoided, however, when the learns to represent words in a highly selective manner, for example, if one unit codes for the word RACHEL, another for MONICA, and yet another JOEY, there is no ambiguity when the three units are co-activated.

Professor Bowers said: "Our research provides a possible explanation for the discovery that single neurons in the cortex respond to information in a highly selective manner. It's possible that the cortex learns highly selective codes in order to support short-term memory."

The study is published in Psychological Review.

add to favorites email to friend print save as pdf

Related Stories

Mapping objects in the brain

Dec 20, 2013

A brain region that responds to a particular category of objects is found to consist of small clusters of neurons encoding visual features of these objects.

Researchers discover key to the reduction of forgetting

Dec 12, 2013

A team of neuroscientists has found a key to the reduction of forgetting. Their findings, which appeared in the journal Neuron, show that the better the coordination between two regions of the brain, the less likely we are ...

Brain processes written words as unique 'objects'

Apr 29, 2009

A new study provides direct experimental evidence that a brain region important for reading and word recognition contains neurons that are highly selective for individual real words. The research, published by Cell Press ...

Clouds in the head

May 21, 2013

Many brain researchers cannot see the forest for the trees. When they use electrodes to record the activity patterns of individual neurons, the patterns often appear chaotic and difficult to interpret.

Recommended for you

Steering the filaments of the developing brain

4 minutes ago

During brain development, nerve fibers grow and extend to form brain circuits. This growth is guided by molecular cues (Fig. 1), but exactly how these cues guide axon extension has been unclear. Takuro Tojima ...

Do we really only use 10% of our brain?

54 minutes ago

As the new film Lucy, starring Scarlett Johansson and Morgan Freeman is set to be released in the cinemas this week, I feel I should attempt to dispel the unfounded premise of the film – that we only use 10% of our brains ...

Birthday matters for wiring-up the brain's vision centers

21 hours ago

Researchers at the University of California, San Diego School of Medicine have evidence suggesting that neurons in the developing brains of mice are guided by a simple but elegant birth order rule that allows them to find ...

User comments