Setting the Scene, with Odors
Research using lobsters shows how discontinuous odor information is integrated at the neuronal level to produce an ‘olfactory scene’. It could have practical applications in identifying the location of explosives or drugs.
Rich Whitworth |
Lobsters are known to use odors to detect food, track fellow lobsters and avoid predators but the mechanisms have been obscure. Now a study by Il Memming Park and colleagues at the University of Florida has advanced understanding at the neuronal level of how lobsters perform these tasks.
The team sought to understand how neurons process and represent information by studying the cells’ “spiking activity”, a measure of how they communicate with other neurons and collectively compute. “The olfactory world, unlike the sense of sight or hearing, is perceived through a filament of odor plume riding on top of complex and chaotic turbulence,” Park explains. “This means that you are not going to be in constant contact with an odor.” To illustrate this, consider how you locate a barbeque. While searching for the source of the odor, you are not always in direct contact with the smell but instead follow ‘waves’ of increasingly intense odor.
“Lobsters heavily depend on their ability to constantly analyze olfactory sensory information to form an olfactory scene,” Park continues. “One critical component for olfactory scene analysis is the temporal structure of the odor pattern. We wanted to find out how neurons encode and process this information.”
The neurons under investigation were a group of rhythmically active primary olfactory receptor neurons (ORNs) called bursting ORNs (bORNs), which detect odor signals to be processed by downstream neurons. “It is very surprising that those neurons seemed to be spontaneously generating signals even after the odor stimuli disappears,” says Park, “We wanted to understand why a sensory system would generate its own signal – especially as the downstream neurons would not know if the signal was genuine or not”. The group came to realize that the neurons acted like tiny clocks; when the neuron is stimulated by external odor molecules, it repeats the signal in a time-dependent manner. “Each neuron is too noisy to be a precise clock, but there is a whole population of these neurons such that together, they can measure those temporal aspects critical for olfactory scene analysis,” Park explains. In some ways, the system has parallels to the echolocation (bio sonar) used by bats and dolphins.
Can research on lobster neurons be applied to electronic nose (E-nose) technology? Typically, E-noses focus on discriminating ‘what’ the odor is. However, in the case of dangerous chemicals, such as explosives or potent drugs, the location of the source could prove invaluable.
“We show how animals might use the ‘when’ information to reconstruct the ‘where’ information (the olfactory scene),” says Park, “Such knowledge could inspire neuromorphic chips full of artificial neurons using the same principle to encode temporal intervals into instantaneously accessible information.”
- I. M. Park et al., “Intermittency coding in the primary olfactory system: A neural substrate for olfactory scene analysis”, J. Neurosci, 34 (3) 941-952 (2014).