Abstract
We all have a sense of time. Yet, there are no sensory receptors specifically
dedicated for perceiving time. It is an almost uniquely intangible
sensation: we cannot see time in the way that we see color, shape,
or even location. So how is time represented in the brain? We explore
the neural substrates of metrical representations of time such as
duration estimation (explicit timing) or temporal expectation (implicit
timing). Basal ganglia (BG), supplementary motor area, cerebellum,
and prefrontal cortex have all been linked to the explicit estimation
of duration. However, each region may have a functionally discrete
role and will be differentially implicated depending upon task context.
Among these, the dorsal striatum of the BG and, more specifically,
its ascending nigrostriatal dopaminergic pathway seems to be the
most crucial of these regions, as shown by converging functional
neuroimaging, neuropsychological, and psychopharmacological investigations
in humans, as well as lesion and pharmacological studies in animals.
Moreover, neuronal firing rates in both striatal and interconnected
frontal areas vary as a function of duration, suggesting a neurophysiological
mechanism for the representation of time in the brain, with the excitatory-inhibitory
balance of interactions among distinct subtypes of striatal neuron
serving to fine-tune temporal accuracy and precision.
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