FV 2 Mapping encoding and flow of task-relevant information from human MEG recordings in a perceptual decision-making task

Background: What are the brain computations used to take appropriate
decisions based on the available sensory evidence? Recordings
of cortical population activity of subjects performing perceptual discrimination
tasks have begun to reveal the distribution across brain
areas and frequency bands of neural signals encoding the sensory
stimulus or the subject’s decision (Wilming et al., Nat. Commun.,
2020), as well as mapping the transmission of activity between
selected pairs of visual regions (Bosman et al., Neuron, 2012; Ferro
et al., PNAS, 2021). Despite this progress, a comprehensive and quantitative
large-scale mapping of both information encoding and transmission
during perceptual decisions is still lacking.
Objective: Our objective is to perform a complete identification of
when and how sensory information is encoded in the cortical hierarchy
and in the frequency activity space, how it is transmitted to
other brain areas, and how is used to guide behavioral choice.
Methods: We analysed published whole-brain MEG recordings
(Wilming et al., Nat. Commun., 2020) from human participants performing
a visual contrast discrimination task entailing a sequence of
10 discrete sample stimuli whose contrast had to be averaged and
compared to a reference. We used mutual information to quantify
stimulus and choice information in brain activity across time, frequency,
and 180 regions per hemisphere covering the entire cortex.
We used Intersection Information (II, Pica et al., NIPS, 2017) to quantify
how much of the sensory information encoded in neural activity
is used to inform choices. Moreover, we measured the amount of
information about stimulus or choice transmitted between cortical
areas using our newly developed Feature-specific Information
Transfer (FIT) measure.
Results: We identified frequency bands that carried stimulus, choice,
and intersection information across cortex. Stimulus information
used to inform choices was initially carried in the gamma-band,
[40, 80) Hz, in visual, parietal and posterior cingulate regions.
Choice signals later developed in the alpha-/beta-bands, [8, 40) Hz,
in downstream regions of premotor and somato-motor cortex. The
region-specific time-frequency patterns of information accurately
predicted the region’s placement in the anatomical hierarchy and
had distinguishable profiles for different anatomical groups.
Stimulus-specific and choice-specific information were broadly
transmitted across many areas, with transmission of stimulus information
occurring predominantly in the feedforward direction in the
gamma-band, and transmission of choice information predominantly
in the feedback direction in the alpha-/beta-bands.
Conclusions: Using information theory, we mapped the encoding
and transmission of task-relevant variables across frequency and
cortical locations in the human brain during a perceptual discrimination
task. This revealed a transformation over time of stimuluinformation in the gamma band in visual, parietal and cingulate
areas into choice signals in the beta and alpha band in downstream
areas, mediated by distributed patterns of feedforward gamma stimulus
information and feedback alpha-beta choice information
transmission.