The function of neuronal oscillations over sensory cortices; collecting evidence from a combined behavioural-electrophysiological study

One of the things that distinguishes humans from lower animals is their ability to select task-relevant information in cluttered sensory environments. This ability goes beyond merely selecting the information to which one has to respond; it also involves the ability to deal with the conflict that emerges when multiple stimuli elicit incompatible responses. This response conflict results from insufficient selection between the different stimuli. Of course, at some point, this conflict has be resolved; otherwise, no response would be given. The dominant view is that the conflict is resolved by a stronger stimulus selection (i.e., enhancing task-relevant information and blocking distractors). One of the central questions in cognitive neuroscience is how the brain achieves this selective gating of sensory information in interaction with the detection of response conflict.

A dominant view is that neuronal oscillations play a central role in this gating of sensory information. This starts from the common observation of alpha band (8-14 Hz) oscillations over posterior (occipito-parietal) areas and alpha- and beta band (15-25 Hz) oscillations over sensorimotor areas. With respect to the functional role of these oscillations, the dominant view involves that high amplitude neuronal oscillations block the sensory input (visual for the posterior and somatosensory for the sensorimotor areas) whereas low amplitude oscillations allow the sensory input to be transferred to the downstream areas that are responsible for cognitive control and motor output. It is surprising how little evidence there is for the claim that these oscillations effectively gate the transfer of sensory input to these downstream areas. It is the goal of this project to provide such evidence. We will conduct a study in which we will investigate this gating function in the visual modality. We will characterize the relationship between alpha band oscillations over posterior areas and three variables that index cognitive control motor output: (1) the behavioural output itself, involving reaction time and accuracy, (2) a frontal evoked response (the N2) indexing response conflict, and (3) a neuronal precursor of overt motor behaviour, modulations of beta-band oscillations over sensorimotor cortex.

In our experiment, we will use a stimulus configuration that mimics everyday visual scenes. These scenes typically involve multiple streams with varying content, of which only a subset is behaviourally relevant at any given time. In our experiment, the participant fixates the center of the screen while stimulus streams are presented in the left and the right visual field. The streams are continuously present but their content varies over time. The streams' content are symbols (e.g., letters and digits) belonging to one of three different categories associated with a button press: press left (e.g., an odd digit), press right (e.g., an even digit), and don't press (e.g., a letter). The participant's task is to respond as quickly as possible when a press left or a press right symbol shows up in the attended stream. By shortening the presentation time and by means of feedback, response speed will be stressed, thereby increasing the probability of an error. By means of a cue, one of these two streams will be indicated as the task-relevant one (also denoted as the attended one), and the other one will be the distracter.

From the perspective of the functional role of posterior alpha band oscillations, four trial types can be distinguished:

  1. Trials in which one of the streams shows a press symbol, and
    1. this stream is the attended one (and the press symbol a target)
    2. this stream is the non-attended one (and the press symbol a distractor)
  2. Trials in which two of the streams show a press symbol, and
    1. in the press symbols are congruent (same response button indicated)
    2. in the press symbols are incongruent (different response button indicated)

We will investigate the relation between posterior alpha band oscillations in the pre-stimulus (press symbol) interval and three post-stimulus variables:

  1. The behavioural response, which has aspects accuracy and reaction time.
  2. A frontal evoked response (the N2) indexing response conflict.
  3. A neuronal precursor of overt motor behaviour, modulations of beta-band oscillations over sensorimotor cortex

We predict the following relations between alpha power and these post-stimulus variables:

  1. Alpha power over the contralateral hemisphere (contralateral to the attended stimulus stream) is negatively related with
    1. accuracy and speed
    2. the frontal N2 amplitude (in incongruent trials)
  2. Alpha power over the ipsilateral hemisphere is positively related with
    1. accuracy and speed
    2. the frontal N2 amplitude (in incongruent trials)
    3. the beta-band power over the motor cortex that is indicated by the distractor press symbol

This project will be supervised by Eric Maris.