Fig. 1
From: Spatial scale of receptive fields in the visual sector of the cat thalamic reticular nucleus
Neural circuits and sample recordings from the visual thalamus (PGN and LGN) of the cat. a The PGN and main layers of the LGN drawn as rectangles including populations of excitatory (light fill) and inhibitory neurons (dark fill). Glutamatergic synapses (open arrows); GABAergic synapses (filled circles) and electrical synapses (resistor). b Parasagittal section of the visual thalamus; the layers of the LGN (gray) and the PGN (blue). Red lines and corresponding text mark retinotopic position7; dashed box illustrates a single retinotopic location sampled by the multi-electrode. c Nissl-stained coronal section showing a recording site (red arrow). d Recordings from a neuron in the PGN (blue) and a relay cell in the LGN (black) with bursts (red) shown at an expanded time scale. Illustrations of the (e) thermostat and (f) searchlight hypotheses. Boxes with dashed outlines represent local circuits for adjacent regions of the visual field; excitatory, inhibitory, and electrical synapses as above. For the thermostat hypothesis (e), reticular feedback has a net inhibitory affect, homogenizing thalamic activity (bottom bar graph) by suppressing peaks of activity driven by feedforward input. Because single reticular neurons must sense distributed thalamic activity, their receptive fields (top) are larger than those of a thalamic relay cell (bottom). For the searchlight hypothesis (f), reticular feedback exerts a net positive effect, enhancing local activity in the thalamus (bottom bar graph) through rebound excitation. Because reticular neurons signal top-down attentional spotlights, their receptive fields sizes (top) are comparable to those in the LGN (bottom)
