SIMULTANEOUSLY RECORDED SINGLE UNITS IN THE FRONTAL-CORTEX GO THROUGHSEQUENCES OF DISCRETE AND STABLE STATES IN MONKEYS PERFORMING A DELAYED LOCALIZATION TASK
E. Seidemann et al., SIMULTANEOUSLY RECORDED SINGLE UNITS IN THE FRONTAL-CORTEX GO THROUGHSEQUENCES OF DISCRETE AND STABLE STATES IN MONKEYS PERFORMING A DELAYED LOCALIZATION TASK, The Journal of neuroscience, 16(2), 1996, pp. 752-768
To test whether spiking activity of six to eight simultaneously record
ed neurons in the frontal cortex of a monkey can be characterized by a
sequence of discrete and stable states, neuronal activity is analyzed
by a hidden Markov model (HMM). Using the HMM method, we are able to
detect distinct states of neuronal activity within which firing rates
are approximately stationary. Transitions between states, as expressed
by concomitant changes in the firing rates of several units, occur qu
ite abruptly, The significance and consistency of the states are confi
rmed by comparison with simulated data. The detected states are specif
ic to a monkey's response in a delayed localization task, allowing cor
rect prediction of the response in similar to 90% of the trials. Simil
ar predictive power is achieved by a model based simply on the respons
e histograms (PSTH) of the units. The two models reach this predictive
ability with different time courses: the PSTH model gains predictive
power with a higher rate in the first second of the delay, and the HMM
gains predictive power with higher rate in the next 3 sec, In this la
ter period, conventional methods such as the PSTH cannot detect any fi
ring rate modulations, but the HMM successfully captures transitions b
etween distinct states that are specific to the monkey's behavioral re
sponse and occur at highly variable times from trial to trial. Our res
ults suggest that neuronal activity in this later period is described
best as transitions among distinct states that may reflect discrete st
eps in the monkey's mental processes.