Our understanding of the neural mechanisms underlying perception and cognition
has been limited by the lack of tools to modulate the activity of specific neural
circuits in the awake animal. This has, in turn, limited our understanding of
devastating disorders of the nervous system that result from miswiring of neural
circuits. Recent advances in optogenetic techniques have begun to make this
level of control possible in the mouse. However, mice are difficult to train,
and the mouse brain differs substantially from the primate brain. While the
rhesus macaque has traditionally been the model system of choice for studying
perception and cognition, smaller new world primates, such as the marmoset
(Callithrix jacchus), offer many advantages including the potential to develop
transgenic lines (Sasaki et al., 2009). Developing such lines would bring optogenetic tools now
fruitfully being used to tease apart circuits of the mouse brain to bear on
understanding the brains of non-human primates. But a critical question is
whether marmosets can perform behavioral tasks when the head is stabilized,
which both facilitates neuronal recording as well as the measurement and
control of eye movements. The goal of the proposed project is to test this.
This will be a critical step in the development of transgenic primate lines
for neuroscience research. In addition, because the cost and health risks
associated with the marmoset are small, in comparison to the macaque, this
will open new avenues of research to the broader neuroscience community.
Funding provided by the Kavli Institute for Brain and Mind at UCSD.
Video demos of an awake marmoset in a fixation task. Each trial
begins with a central fixation point (shown in white). A low contrast purple ring
is superimposed on the video screen, and indicates the fixation position of the
marmoset. After fixation is acquired on the central point, Gabor stimuli are flashed
in the periphery for 1-2 seconds. If the marmoset holds fixation through this period
then a picture of a marmoset face is shown, a bell tone is rung, and a juice reward is
given. If the marmoset breaks from fixation a gunshot sounds is played and no reward
Video demo of awake marmoset delaying a saccade to a peripherally cued
location for reward. Again, his fixation is indicated by a very low contrast
purple ring (you may have to squint). Each trial begins with a white fixation
point flashing. Once fixation is acquired the fixation point stops flashing,
and then the marmoset must hold fixation at the center while a peripheral
target in one of four apertures is flashed. After 600-1000 ms the fixation
point turns black, indicating it is allowed to saccade to the peripheral
stimulus for reward.
This task is a first step towards covert attention tasks. Unlike the
fixation demo above, reward is not delivered at fixation but instead is
associated with a cued peripheral location. The natural response is to make
a saccade to the rewarded location, but this must be inhibited until the
central fixation is extinguished.
Video demo of awake marmoset selecting a vertical oriented grating
from distracter stimuli of a similar orientation. Again, fixation is shown
by a low contrast purple ring, and his choice indicated by a saccade.
Video demo of awake marmoset selecting a tilted grating from a set
of horizontal distracter stimuli. Tilts varied in magnitude from trial to trial.
Again, fixation is shown by a low contrast purple ring, and his choice
indicated by a saccade.