The position, size, and shape of the receptive
field (RF) of some cortical neurons change dynamically,
in response to artificial scotoma conditioning (Pettet
& Gilbert, 1992) and to retinal lesions (Chino et al.,
1992; Darian-Smith & Gilbert, 1995) in adult animals.
The RF dynamics are of interest because they show how visual
systems may adaptively overcome damage (from lesions, scotomas,
or other failures), may enhance processing efficiency by
altering RF coverage in response to visual demand, and
may perform perceptual learning. This paper presents an
afferent excitatory synaptic plasticity rule and a lateral
inhibitory synaptic plasticity rule—the EXIN rules
(Marshall, 1995)—to model persistent RF changes after
artificial scotoma conditioning and retinal lesions. The
EXIN model is compared to the LISSOM model (Sirosh et al.,
1996) and to a neuronal adaptation model (Xing & Gerstein,
1994). The rules within each model are isolated and are
analyzed independently, to elucidate their roles in adult
cortical RF dynamics. Based on computer simulations, the
EXIN lateral inhibitory synaptic plasticity rule and the
LISSOM lateral excitatory synaptic plasticity rule produced
the best fit with current neurophysiological data on visual
cortical plasticity in adult animals (Chino et al., 1992;
Pettet & Gilbert, 1992; Darian-Smith & Gilbert,
1995) including (1) the retinal position and shape of the
expanding RFs; (2) the corticotopic direction in which
responsiveness returns to the silenced cortex; (3) the
direction of RF shifts; (4) the amount of change in response
to blank stimuli; and (5) the lack of dynamic RF changes
during conditioning with a retinal lesion in one eye and
the unlesioned eye kept open, in adult animals. The effects
of the LISSOM lateral inhibitory synaptic plasticity rule
during artificial scotoma conditioning are in conflict
with those of the other two LISSOM synaptic plasticity
rules. A novel “complementary scotoma” conditioning
experiment, in which stimulation of two complementary regions
of visual space alternates repeatedly, is proposed to differentiate
the predictions of the EXIN and LISSOM rules.