The Journal of Neuroscience, March 1, 2003, 23(5):1903
Representation of Odor Habituation and Timing in the
Hippocampus
Sachin S.
Deshmukh and
Upinder S.
Bhalla
National Centre for Biological Sciences, Gandhi Krishi Vignana
Kendra Campus, Bangalore 560065, India
We performed simultaneous single-neuron recordings from the
hippocampus and the olfactory bulb of anesthetized, freely breathing rats. Odor response properties of neurons in the olfactory bulb and
hippocampus were characterized as firing rate changes or
respiration-coupled changes. A panel of five odors was used. The rats
had not been exposed to the odors on the panel before the experiment.
The olfactory bulb and hippocampal neurons responded to repeated odor
presentations in two ways: first, by changes in firing rate, and
second, by respiratory tuning changes. Approximately 60% of bulbar
neurons, 48% of hippocampal CA1 neurons, and 12% of hippocampal CA3
neurons showed statistically significant responses. None of the
odor-responsive neurons in either the bulb or hippocampus responded to
all of the odors on the panel. Repeated 10 sec odor stimuli presented at the intervals of 20, 30, 60, 110, and 160 sec were used to analyze
the effect of the interval on odor response properties of the recorded
neurons. Bulbar neurons were relatively nonselective for odor interval.
Hippocampal neurons showed unexpected selectivity for the interval
between repeated odor presentations. CA1 and CA3 neurons responded to
only one to three of the intervals in the range. On the basis of these
findings, we postulate that the hippocampus has the ability to keep
track of the time elapsed between consecutive odor stimuli. This may
act as a neuronal substrate for habituation and for complex tasks such
as odor-guided navigation.
Key words:
olfactory bulb; hippocampus; odor; odor
selectivity; habituation; information processing; representation; electrophysiology; single-neuron recording
Copyright © 2003 Society for Neuroscience 0270-6474/03/2351903-13$05.00/0