Welcome to the new year all!
The first Dart NeuroScience seminar of 2015 will feature Dr. Leonard Maler from the University of Ottowa giving the Founder’s Day Lecture in honor of Dr. Theodore Bullock. Dr. Maler’s work focuses on the electrosensory system of the brown ghost knife fish, Apteronotus Leptorhynchu, employing morphological, electrophysiological, and computational techniques to better understand the way in which these fish process information about their environment.
Specifically, in a recent paper titled “Enhanced sensory sampling precedes self-initiated locomotion in an electric fish” his group suggests that volition, the ability to make a conscious decision to carry out an action, may be a capability earlier evolved than previously thought, present in aquatic vertebrates whose latest common ancestor with primates dates back to more than 450 million years ago! (Jun et al.) Wow time really flies.
Different life forms sense and interpret their environment in different ways. Take for example a human being who has resolved to hit the gym in the new year: she walks in and immediately sees the horde of fellow gym-goers, smells the running partner next to her, hears the powerlifters in all their grunting glory (the joys of gym-ing, right?) These are examples of active sensing behaviors that typically occur when animals are exploring an environment.
Now, let’s imagine we are brown ghost knife fish interacting with our Amazonian surroundings: given the dark underwater environment we’ll need to rely on a different sense to help us navigate around rocks and find tasty food. So, we fire up the electric organ and discharge pulses of electricity that stimulate electroreceptors on the skin. No predators or prey nearby if there’s no disturbance in the force, but if you sense a distortion in the electric field, look out! It could be lunch if we’re lucky, and open jaws if we’re not. For a more detailed explanation of their electric fish, check out the lab page here.
Since these electric organ discharges (EOD) can be measured and temporally mapped to movement, this could be a great way to answer the questions Dr. Maler has regarding volition, decision making, and active sensing in the electric fish. Check out this cool experimental setup:
Experimental tank in a sensory-isolation chamber with infrared (IR) lighting. Electric organ discharge (EOD) signal was captured by eight dipoles symmetrically placed around the edge of the tank to monitor the EOD rate (EODR) and movement activity; a video camera also directly captured movement. Subwoofers delivered random stimuli during a sensory-evoked condition and a microphone was used to record possible noise contamination.
Should I stay or should I go now?
Being the first week of a new year, a lot of us might have made decisions to get fit, save money, or volunteer more, but what about the more constant and subtle decisions regarding movement? Voluntary actions are a sort of decision making by which an animal chooses to enact a certain movement; they are typically exploratory behaviors (not having been caused by an unexpected stimulus) and are generally random (predictability would make it too easy for a predator).
It has been shown that in humans, cortical activity and an increase in sensory information acquisition precedes voluntary movement, however, the temporal dynamics of sensory sampling and movement initiation had not previously been established in electric fish. Alas! Dr. Maler’s group has shown a similar preparatory sensory acquisition in electric fish, and that this behavior had a random occurrence, exhibiting behavioral variability, two of the characteristics aforementioned in defining voluntary actions and decision making!
Fig. 4. Increase in the sensory sampling rate precedes voluntary movement. (A,B) Pseudo-colour plots of the normalized EOD Rate (A) and the EOD Acceleration (B) time courses during spontaneous (top) and sound-evoked (middle) transitions. Time 0 indicates the movement onset, and trials are ordered by their EOD Rate up-transition onsets. Bottom, trial-averaged EOD Rate and EOD Acceleration normalized by the peak; both exhibited striking differences between spontaneous (green traces) and evoked (magenta traces) transitions.
The fish studied by Maler’s group display two behavioral states, defined as up-state and down-state (electrically active and non-active). Dr. Maler and colleagues saw self-initiated onsets of activity, associated with periods of increased preparatory sensory sampling rate (occurring up to 5 seconds prior to activity), which suggests that the animal is in a heightened sensory state and exhibiting exploratory behaviors! (Jun et al., Fig. 4) They conclude that this activity may represent volition in Apteronotus Leptorhynchu, that the neural processing occurring before self-initiated movement bears similarity to that in humans, and suggest the telencephalon as a possible region for further investigation. Given the homologies between teleost fish and mammalian telencephali, further study into the neural regions and mechanisms involved in modulating up-state activity in these fish could give insights into human neural circuitry involved in voluntary actions, sensory acquisition, and decision making. Tune in on Tuesday to find out more!
If your new year’s resolutions include enjoying more awesome science, then join us Tuesday, January 6th at 4pm in the CNCB large conference room for what’s sure to be an interesting Founder’s Day Lecture given by Dr. Leonard Maler, titled: “And now for something completely different: Active sensing, learning and recurrent networks in the telencephalon of a weakly electric fish.”
Nicole Hoffner is a first year Neurosciences student currently rotating with Dr. Bradley Voytek. She spends her spare time reading or sleeping, enjoys fishing on occasion, and wonders what an electric fish tastes like.
Jun J.J., Longtin A. & Maler L. Enhanced sensory sampling precedes self-initiated locomotion in an electric fish., The Journal of experimental biology, PMID: http://www.ncbi.nlm.nih.gov/pubmed/25320268