Figure 1. Functional macrocircuit of key brain processes and regions that are currently being developed in CNS neural models of visually-based intelligence. LGN = Lateral Geniculate Nucleus; V1 = striate visual cortex; V2, V4, MT, MST = prestriate visual cortex; IT = inferotemporal cortex; PPC = posterior parietal cortex; PFC = prefrontal cortex.
Figure 2: A LAMINART cortical circuit. Excitatory neurons are open symbols, inhibitory interneurons are shown filled-in black. (a) The LGN provides bottom-up activation to layer 4 via two routes. (b) Folded feedback carries attentional signals from higher cortex into layer 4 of V1, via the modulatory 6-to-4 path. (c) Connecting the 6-to-4 on-center off-surround to the layer 2/3 grouping circuit. (d) Top-down feedback from V1 layer 6 to LGN also has an on-center off-surround anatomy, similar to the 6-to-4 path. (e) The entire V1/V2 circuit: V2 repeats the laminar pattern of V1 circuitry, but at a larger spatial scale. See Grossberg and Raizada (2000) at www.cns.bu.edu/ Profiles/Grossberg for detailed discussion and extensive experimental support.
Figure 3: A laminar
model of basal ganglia interactions with the FEF and the SC. Key: I-VI
are cortical laminae; Va and Vb, respectively, are superficial and deep layer
V. Subscripts xy are grid coordinates, whereas subscript i denotes mapping
module (Figure 4). All variables for FEF activities use the symbol F.
Processed visual inputs 
and 
emerging
from visual areas including V4 and posterior IT feed into the model FEF input
layer and affect activations F(I)xyi. This
layer is predicted to reside in layer III and possibly parts of layers II and
IV. Visual input also excites the PPC, Pxy, and anterior
IT, Tk (visual input path not shown). A motivational
signal I(M) arouses working memory activity Ci,
which in turn provides a top-down arousal signal to model FEF layer VI cells,
with activities F(G)i. The input layer activities
F(I)xyi excite cells F(P)xyi
in the plan layer, which is predicted to reside in layers III/Va and possibly
part of layer II. In the plan layer, different motor responses are planned
to the input signal, e.g. a saccade to the target or to the fixation point.
FEF layer VI activities F(G)i excite the groups/categories
of plans associated with mapping module i. The basal ganglia decide
which plan to execute and send a corresponding gating signal to the thalamus
Vk, which activates model layer Vb output cells (F(O))
to execute the plan. The model distinguishes (Kemel et al., 1988) a thalamus-controlling
basal ganglia pathway, whose variables are symbolized by B, and a colliculus-controlling
pathway, whose variables are symbolized by G. Thus, the striatal
direct (SD) pathway activities B(SD)k and
G(SD)xy respectively inhibit GPi activities B(GPi)k
and SNr activities G(SNr)xy, which respectively
inhibit thalamic activities Vk and collicular activities Sxy.
If the FEF saccade plan matches the most salient sensory input to the PPC, then
the basal ganglia disinhibit the SC to open the gate and generate the saccade.
However, if there is conflict between the bottom up input to PPC and the top-down
planned saccade from FEF, then the basal ganglia-SC gate is held shut by feedforward
striatal inhibition until the cortical competition resolves. The saccade
signal then activates PPC and the SC (Sxy). The SC excites
FEF postsaccadic cell activities F(X)xy, which
delete the executed plan activity. Filled semi-circles terminate cortico-striatal
and cortico-cortical pathways modeled as subject to learning that is modulated
by reinforcement-related dopaminergic signals (dashed arrows).