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1. Neural correlates of motor
preparation
Project: fMRI study of motor
preparation
Principal Investigator: P. Read Montague
Collaborators: David Eagleman (Baylor College of Medicine)
Chess Stetson (Caltech)
What happens when the brain
awaits a signal of uncertain arrival time, as when a sprinter
waits for the starting pistol? We here report a novel type of
neural signature: blood flow in the supplementary motor area
remains at baseline during the readiness period and then rises
only after the 'go' signal. The amplitude of this delayed
response depends on the length of the preceding readiness
period: longer preparation causes higher blood flow. The
dependence of the amplitude on the readiness period is not a
consequence of motor output, but is equally evident in no-go
conditions. The amplitude is modulated by expectations of the
arrival time of the go signal, appearing to encode a
cumulative conditional probability (also known as the
cumulative hazard function). This encoding is not dependent on
modality, operating in the same manner with auditory and
visual signals. We suggest that anticipation of a temporally
uncertain signal leads to an increasing energy debt which must
be "paid back" with blood flow after the readiness period has
ended.
2. Neural correlates of
visual imagery vividness
Project: fMRI study of motor
preparation
Principal Investigator: P. Read Montague
Collaborators: David Eagleman (Baylor College of Medicine)
Cameron Jeter (University of Texas, Houston), Dongni Yang
(Baylor College of Medicine)
When asked to imagine a visual
scene, such as an ant crawling on a checkered table cloth
toward a jar of jelly, individuals subjectively report
different vividness in their mental visualization. Can we
measure such vividness objectively? We show that reported
vividness is correlated with the early visual cortex activity
relative to the whole brain activity measured by fMRI: the
higher visual cortex activity is, the more vivid the imagery
is.
Cui, X., Jeter, C.B., Yang,
D., Montague, P.R., and Eagleman, D.M. (2007) Vividness of
mental imagery: individual variability can be measured
objectively. Vision Research 47, 474-478
link to full text
3. Temporal Perception
Project: fMRI study of temporal order reversal illusion
Principal Investigator: P. Read Montague
Collaborators: David Eagleman (University of Texas, Houston)
Chess Stetson (University of Texas, Houston)
To judge causality, organisms must determine the temporal
order of their actions and sensations. However, this
judgment may be confounded by changing delays in sensory
pathways, suggesting the need for dynamic temporal
recalibration. To test for such a mechanism, we artificially
injected a fixed delay between participants¡¯ actions (keypresses)
and subsequent sensations (flashes). After participants
adapted to this delay, flashes at unexpectedly short delays
after the keypress were often perceived as occurring before
the keypress, demonstrating a recalibration of motor-sensory
temporal order judgments. When participants experienced
illusory reversals, fMRI BOLD signals increased in anterior
cingulate cortex/medial frontal cortex (ACC/MFC), a brain
region previously implicated in conflict monitoring. This
illusion-specific activation suggests that the brain
maintains not only a recalibrated representation of timing,
but also a less-plastic representation against which to
compare it.
Stetson, C., Cui, X.*,
Montague, P.R., and Eagleman, D.M. (2006). Motor-sensory
recalibration leads to an illusory reversal of action and
sensation. Neuron 5, 651-659.
*parallel first author
link to full text
4. Dopamine model
Project: Extracellular dopamine dynamics model
Principal Investigator: P. Read Montague
Collaborators: John Dani, Fuming Zhou
Information encoded as spike trains (digital signal) is
decoded as extracelluar dopamine concentration fluctuation
(analog signal) in dopamine neurons. What is the decoding
method, what is the decoding mechanisms and why does nature
favor this decoding mechanism? To answer these questions, we
built an extracellular dopamine dynamics model and fitted
the model to in-vivo data. We plan to fit the model to the
in-vitro data collected in Dani lab.
5. Extracellular calcium signaling
Project: Fisher information of cleft calcium signal
Principal Investigator: P. Read Montague
Cleft calcium concentration significantly drops as a
consequence of calcium influx during an action potential at
presynaptic bouton. This drop occurs even if the
neurotransmitter is not released. Is neurotransmitter
release failure a waste? Is the calcium drop a signal and
how good is this signal? We plan to answer this question by
calculating the fisher information of this cleft calcium
signal.
6. Energy usage efficiency in neural signaling
Why is the amplitude of an action potential is 100 mV? Both information and energy might have shaped the size of action potentials during evolution.
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