Behavioural and neuronal correlates of sensory prioritization in the rat whisker system
Date
2017
Authors
Lee, Conrad
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Abstract
Animals need to assess when to initiate actions based on
uncertain sensory evidence. To formulate a response, decision
making systems must prioritize extraction of neuronal signals
that represent ecologically relevant events from signals that are
behaviorally less relevant. This is commonly known as selective
attention. The current thesis aims to investigate two simple
forms of attention in rodents: sensory prioritization to a
specific modality and temporal cueing. The rat whisker system is
functionally efficient, and anatomically well characterized. We
therefore utilize the whisker touch as a model sensory system to
investigate the neuronal and behavioral correlates of attention
in rats.
We begin this thesis by designing a novel simple detection task
that investigated whether rats dedicate attentional resources to
the sensory modality in which a near-threshold event is more
likely to occur. Detection of low-amplitude events is critical to
survival, and to formulate a response, animals must extract
minute neuronal signals from the sensory modality that is more
likely to provide key information. We manipulated attention by
controlling the likelihood with which a stimulus was presented
from one of two modalities. In a whisker session, 80% of trials
contained a brief vibration stimulus applied to whiskers and the
remaining 20% of trials contained a brief change of luminance.
These likelihoods were reversed in a visual session. When a
stimulus was presented in the high-likelihood context, detection
performance increased and was faster compared with the same
stimulus presented in the low-likelihood context. Sensory
prioritization was also reflected in neuronal activity in the
vibrissal area of primary somatosensory cortex: single units
responded differentially to a whisker vibration stimulus when
presented with higher probability compared to the same stimulus
when presented with lower probability. Neuronal activity in the
vibrissal cortex displayed signatures of multiplicative gain
control and enhanced response to vibration stimuli during the
whisker session. In Chapter 3, we replicated these findings in a
forced choice paradigm and extended the investigation from
somatosensory/visual to the somatosensory/auditory. Attention was
similarly manipulated by controlling likelihoods of stimulus
presentation. Again, we observed improvements in detection
performance and reaction time, as well as improvements in
discrimination performance for stimuli presented in a
high-likelihood context. The behavioral consequences of a forced
choice compared to simple detection task are discussed.
Finally, we developed a novel task that investigated whether rats
were able to dedicate attentional resources in time. Operating
with some finite quantity of attentional resources, by direct
these resources at the expected time, animals would benefit from
prioritizing processing based on temporal cues. We manipulated
temporal cueing by presenting an auditory cue that preceded a
target vibration stimulus in a subset of trials. On another
subset, no auditory cue was presented. Presentations of these
trials were of equal probability. Critically in this paradigm,
the auditory cue provided temporal information but did not
provide any spatial information about the location of the
vibration stimulus. The auditory cue increased detection and
discrimination performances and resulted in faster responses
compared to trials in which the cue was absent. We observed
neuronal signatures of temporal cuing in the vibrissal area of
the primary somatosensory cortex. Single units showed enhanced
response to the vibration stimulus during trials in which the
stimulus was temporally expected. However, we did not observe
signatures of multiplicative gain control in this paradigm.
Instead, a decrease in baseline activity was observed that was
phase locked to the onset of the auditory cue.
In summary, this thesis presents two novel paradigms to study
selective attention in rats in the form of sensory prioritization
and temporal cueing. In addition, we investigate the neuronal
correlates of selective attention in the vibrissal area of the
primary somatosensory cortex. These series of experiments
establish the rat as an alternative model organism to primates
for studying attention.
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Keywords
sensory, prioritization, prioritisation, attention, whisker, system, cortex, somatosensory, multisensory, auditory, vibrissal, visual, tactile, rats, behaviour, behavior, temporal, cueing, recording, extracellular, detection, discrimination, neuronal, neuron
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