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Abstract:
Abstract: Stochastic motion displays have been widely used in
human psychophysics and monkey electrophysiology, yet little is
known about the responses they evoke in the human brain.
Characterizing such responses may contribute to an appreciation of
the relationship between population activity measured by functional
MRI (fMRI) in humans and single unit recordings in monkey V5/MT. We
therefore quantified, using fMRI, how human brain responses depend
on the strength of motion signal (coherence) of these displays.
Activity in human V5/MT showed a strong, highly linear, correlation
with stimulus coherence. In contrast, motion-sensitive areas
posterior to V5/MT showed a highly nonlinear U-shaped response
function. While responses in V5/MT increased as a function of
increasing stimulus coherence, anterior cingulate and other frontal
cortical areas showed the opposite pattern, with decreased
activity. Our findings demonstrate previously unknown dissociations
in the functional properties of human motion areas. Almost linear
BOLD responses to stochastic motion displays, such as we observed,
are predicted from single unit electrophysiological findings using
a remarkably simple linear model of population responses. Thus, the
response of human V5/MT to complex motion stimuli measured by
functional MRI is well characterised by surprisingly simple models,
suggesting that BOLD contrast is directly related to aggregate
neuronal spiking activity. [Supported by the Wellcome Trust and NSF
]
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