the perception of time in animals is easily accomplished by training them on a
variant of a discrete trials fixed-interval schedule of reinforcement, a
procedure known as the peak procedure1.
Briefly, a proportion of trials (50%) are reinforced trials in which food can be
earned for the first operant response following the passage of a criterion duration
(e.g., 10 seconds).
Three information-processing stages required for interval timing are the clock, memory, and decision stages2. The clock stage encompasses the production of a temporal percept, with processes ranging from the generation of a utilizable temporal signal to the integration of this signal into a meaningful output. The value of the clock at the time of reinforcement is stored in long term memory, and is used (decision stage) during future opportunities to earn reward, by comparing whether the current perceived duration (clock) is similar to previously reinforced durations (memory). Reference to this generalized timing model has been used to explain how certain drugs (e.g., the dopaminergic agonist methamphetamine) can alter the perception of time3, (i.e., by increasing the speed of the clock stage), or how certain lesions (e.g., frontal cortex lesions) can systematically alter temporal memory 4.
Recent animal research and functional imaging work in humans has begun to implicate a network of structures, consisting of the frontal and parietal cortices, the striatum, the substantia nigra pars compacta, the output nuclei of the basal ganglia and the thalamus5-8. These structure are connected in a multitude of short and long feedback and feedforward loops as shown in a simplified manner in the figure. However, despite demonstrations showing the activation of these structures during temporal perception tasks, the type of information processed by these structures, as well the specific computations performed in this processing, remain unclear. The primary focus of our lab is to elucidate these neural processes by utilizing a variety of neuroscience techniques, either alone or in combination, including ensemble extracellular recording of multiple neural structures, neurotoxic lesions, and systemic and intra-cerebral drug injections. Combining these neuroscience techniques with behavioral designs and analyses designed to tease out the different processing stages, we hope to decipher the structures, computations, and dynamic interactions underlying the perception of time. In addition to these empirical techniques, we use physiologically constrained computational modeling to both guide experimental designs and help interpret our results4.
2. Church, R.M., Timing and temporal search, in Time and Behaviour: Psychological and Neurobehavioural Analyses, C.M. Bradshaw and E. Szabadi, Editors. 1997, Elsevier: Amsterdam. p. 41-78.
5. Coull, J.T., et al., Functional anatomy of the attentional modulation of time estimation. Science, 2004. 303(5663): p. 1506-8.
6. Leon, M.I. and M.N. Shadlen, Representation of time by neurons in the posterior parietal cortex of the macaque. Neuron, 2003. 38(2): p. 317-27.
7. Matell, M. S. & Meck, W. H. (2004). Cortico-striatal circuits and interval timing: Coincidence-detection of oscillatory processes. Cognitive Brain Research, 21, 139-170.
8. Matell, M.S., W.H. Meck, and M.A. Nicolelis, Interval timing and the encoding of signal duration by ensembles of cortical and striatal neurons. Behav Neurosci, 2003. 117(4): p. 760-73.
3. Meck, W.H., Neuropharmacology of timing and time perception. Brain Research. Cognitive Brain Research, 1996. 3(3-4): p. 227-42.
4. Olton, D.S., Frontal cortex, timing and memory, Neuropsychologia, 1989. 27(1): p.121-130.
1. Roberts, S., Isolation of an internal clock. Journal of Experimental Psychology: Animal Behavior Processes, 1981. 7: p. 242-268.