Impact of Adaptation on Thalamic Neurons' Computational Role of Conveying Contextual Information about Paired-Pulse Tactile Stimuli

Chen Liu

doi:10.17918/etd-7454

Adaptation or the attenuation of neural responses due to the recent history of sensory input has been observed across all sensory modalities. However, computational role of adaptation in conveying sensory information is not completely clear, especially when one considers neural coding problems including discrimination of stimulus location in which adaptation increases the ambiguity of the neural responses about the stimulus's identity. To disentangle this ambiguity, in order to further our understanding of the functional role of adaptation during tactile exploration when an object repeatedly contacts neighboring locations along the tactile organ, we recorded responses from neurons in the rat thalamus while delivering paired stimuli to the whiskers, and quantified the impact of adaption on the representation of information about the stimuli. At the level of single neuron, we found that although adaptation reduces the information about the location of the present stimulus, the adapted response is capable of conveying significant amounts of information about whether, when and where a previous stimulus occurred. Further analysis showed that adaption increases variability of the response across stimuli and this variability conveys increasing amounts of information as the information conveyed by the magnitude of the response decreases. At the level of population neurons, ambiguity of the adapted responses about the present stimulus could be compensated for by large neuronal population size, with more information per spike in the adapted compared to the non-adapted state especially if the identities of each neuron are recognized by the downstream decoder. These results suggest the efficient coding of adaptive population response so that adaptation does not cost the ability to discriminate stimulus location and, more importantly, it gains the capacity to provide information about the spatiotemporal history of the stimulus. However, since the adapted response carries information about the current stimulus as well as the past, it is likely that there is some redundancy (or synergy) in the information about the two stimuli (past and present), potentially ambiguity to completely separate the information about the past stimulus from that of the present from the adapted response. To understand this ambiguity in temporal dimension, we updated our analysis model to include the external and internal source of synergy/redundancy information, and developed expressions for redundancy to explicitly analysis the information contents in the adapted response in the formalism of entropy measurement. The results supported the ability of adapted thalamic neuron to provide information about the stimulus in the past and present simultaneously, in a way that the integrated information about the stimulus pair is not decreased. With the information breakdown. We found that this efficiency in conveying information about the stimulus pair is probably attributed to the adapted response that allowed to encoding the posterior information about the dynamic contexts of the paired stimuli.

Impact of Adaptation on Thalamic Neurons' Computational Role of Conveying Contextual Information about Paired-Pulse Tactile Stimuli

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Impact of Adaptation on Thalamic Neurons' Computational Role of Conveying Contextual Information about Paired-Pulse Tactile Stimuli

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