| |
Abstract:
Abstract: Working memory shows age-related differences when
memory load exceeds capacity. In previous comparative studies
involving younger and older subjects, Rypma & D'Esposito found
that during the retrieval period of high-load working memory tasks
activating dorsolateral PFC reaction time directly correlated with
activation in younger subjects, while the inverse correlation held
for older subjects. We present a model of signal processing in PFC
in which the differences in performance are related to the
discriminability of post-synaptic activation levels, after the
input signal has gone through a sigmoid squashing function. The
observed age-related differences in the relation between activation
levels and performance are explained in this model by setting the
steep region of the squashing functions in different ranges of the
input. In younger subjects, an increase in activation moves the
input range from the optimal region of the squashing function to
the region where the input is constantly high. In older subjects,
an increase in activation moves the input range from the region
where the squashing function has constant low output to the optimal
region. The model individuates a general computational principle
for age-related differences that is applicable to other test
settings.
|
