Has anyone investigated or observed changes in the baseline firing rate of neurons between stimulus applications? I'm specifically interested in the somatosensory domain, but insights from other sensory areas would also be interesting.
The reason I ask this question is the following. Stimulus frequency-dependent changes in the mean firing rate are commonly calculated by integrating the firing rate across a specific time window following stimulus onset for each stimulation condition. If spike rates during the interstimulus intervals change (e.g. due to rebound activity, adaptation of excitatory and/or inhibitory responses), part of the variation in firing rate across stimulation frequencies may be explained by changes in baseline firing rate during stimulation.
I have a sense that I read something related somewhere, but I cannot recall exactly where. Literature suggestions are welcome!
not sure if this answers your question, but your question made me think of stimulus-induced changes in intrinsic excitability. It might be trivial in some sense, but such changes do also then affect the baseline spontaneous firing rate.
You might want to check out the following paper, which shows this directly:
J Neurosci. 2012 Aug 15;32(33):11377-89.
Bidirectional plasticity of intrinsic excitability controls sensory inputs efficiency in layer 5 barrel cortex neurons in vivo.
Mahon S, Charpier S.
You did not specify, what kind of experiments you are performing. If these are in-vivo experiments, then you should consider posible long-term reflexes or e.g. postactivation depression, such as is observed after Ia afferents stimulation (see attached references). To avoid these influences, it is usually sufficient to decrease stimulation rate. If the experiments are conducted on humans during voluntary actions, then it is more complicated, since some changes of voluntary actions may be additionally expected.
Thank you very much for your suggestions. @John Tukker: The study by Mahon and Charpier addresses the question very well I think. @Maria Piotrkiewicz: My experiments involve whisker stimulation in mice and recording in primary somatosensory cortex. I am interested in how neurons respond to a range of stimulus frequencies, therefore reducing the rate is not an option for me. But understanding possible changes in excitability induced by the stimuli is already an important step.
Dear Per Magne Knutsen, many thanks for your answer. I indeed applied stimulus trains at various frequencies. In future experiments I will try out longer interstimulus intervals to control for possible changes in the cellular response. For the current data set, it's unfortunately not an option anymore. I pseudo-randomized the order of stimulus presentation, but I do suspect that there still might be effects of the previous stimuli on the cellular response. I would be curious to know in which frequency range you observe stimulus-evoked changes in excitability that affect the cells' receptive fields. Are you recording in vivo and have you published your observations somewhere?
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