LCNE activity, attention and changes in the environment

Locus Coeruleus (LC) or the blue spot (the name German neuroanatomists Wenzel brothers chose for it in 1812) has Noradrenaline (NA) (also known as Norepinephrine, NE) as its primary transmitter. And the Locus Coeruleus Norepinephrine (LCNE) system has been shown to play a critical role in core behavioural and physiological processes. You can look at this review paper. Or for example, you can look at this recent publication from my colleagues whose results suggest LCNE operates in the same manner as actuators in a control system. It gathers control signals from the controller, amplifies it, and then alters the parameters or connections in the system in order to fulfill the control signals (please note that this analogy is based on my understanding of the paper and my conversations with the lead author, not necessarily the view of the authors of the paper). Given the location of LC, making electrophysiological recordings in it is extremely difficult. But there are a few studies that, based on electrophysiological recordings, have shown that there is a correlation between LCNE activity and pupil diameter. Hence the ever more importance of pupillometry recordings for many neuroscientists, including my own work in this area.

I have worked on the data collected from a set of experiments on set-shifting tasks. The paradigm is as follows. A rat is trained to distinguish between two tones of different frequencies. One is a reward signal. When the rat is trained to distinguish between the two tones, we change the frequencies of the tones, and the rat should figure out which one is the reward signal. This is called Intra-Dimensional Shift (IDS). When the rat learns that, it is faced with a whole new challenge. During the whole period in which the rat was being trained to distinguish between the tones, and then the new set of frequencies after the IDS, there have always been visual stimuli present in its field of view. These stimuli were in the form of moving gratings in different directions. Now, one of these visual stimuli and the tones are irrelevant. This is called Extra-Dimension Shift or EDS. Looking at the pupillometry data and also EEG recordings, we have been able to shed light on some unknown aspects of LCNE activity that is instrumental in attention and how LCNE activity can modulate cortical network in response to changes in the environment.

The effects of manipulating stimulus discriminability on learning, cortical network activity, and neuromodulation

When organisms are uncertain about the consequences of their responses to antecedent stimuli, they learn to adapt by testing new hypotheses and response strategies. Presumably, these cognitive and behavioural responses to uncertainty are driven, at least partly, by uncertainty-evoked noradrenaline release modulating cortical-cortical communication. We found out that, as the rats discover the meanings of the novel stimuli, the modality chosen for hypothesis-testing by the rat depends on their prior experience and that this strategy varies across individuals. In order to study cortico-cortical communication, we analysed coherence between EEG channels. This analysis revealed that, although there is variability across learning strategies of each individual rat, selective interactions occur between the frontal cortex and the sensory cortex representing the modality to which the rat attended. In line with prior human studies on neuromodulation during uncertainty and learning, we observed pupil dilation in response to novel sensory stimuli and during various behavioural strategy changes.

Back to main page.

Vahid S. Bokharaie

Last updated on March 9, 2022. Generated using htlatex.