動物生理学 III

Handout No. 4①②FIGURE 19.21 Receptive Fields of Ganglion
Cells in the retinas of cats and monkeys aregrouped into two main classes: "on"-centerand "off"-center fields. "On"-center cells
respond best to a spot of light shone onto thecentral part of the receptive field. Illumination(indicated by the red bar above records) of thesurrounding area with a spot or a ring of light
reduces or suppresses the discharges andcauses responses when the light is turned off.
Illumination of the entire receptive field elicits
weak discharges because center andsurround antagonize each other's effects, aswith bipolar cells. "Off"-center cells slow down
or stop signaling when the central area of theirfield is illuminated and accelerate when thelight is turned off. Light shone onto thesurround of an "off"-center receptive field
causes ex- citation of the neuron. (AfterKuffler, 1953.)③

Figure 27-4 A simplified diagram of the projections from the retina
to the visual areas of the thalamus (lateral geniculate nucleus) andmidbrain (pretectum and superior colliculus). The retinal projection
to the pretectal area is important for pupillary reflexes, and the projection
to the superior colliculus contributes to visually guided eye movements.
The projection to the lateral geniculate nucleus, and from there to thevisual cortex, processes visual information for perception.

④
Figure 27-6 The lateral geniculate
nucleus is the principal subcorticalsite for processing visual information.
Inputs from the right hemiretina ofeach eye project to different layers of
the right lateral geniculate nucleus tocreate a complete repre- sentation of
the left visual hemitield. Similarly,
fibers from the left hemiretina of eacheye project to the left lateralgeniculate nucleus (not shown). The
temporal crescent is not represented
in contralateral inputs (see Figure27-1 ). Layers 1 and 2 comprise themagnocellular layers; layers 3
through 6 comprise the parvocellularlayers. All of these project to area 17,
the primary visual cortex. (C =contralateral input; I = ipsilateralinput.)

Figure 27-11 Receptive field of a simple cell in the primary visual cortex. The receptive field of acell in the visual system is determined by re- cording activity in the cell while spots and bars oflight are projected onto the visual field at an appropriate distance from the fovea. The records
shown here are for a single cell. Duration of illumination is indicated by a line above each recordof action potentials. (Adapted from Hubel and Wiesel 1959 and Zeki 1993.)
1. The cell's response to a bar of light is strong- est if the bar of light is vertically oriented in thecenter of its receptive field.
2. Spots of light consistently elicit weak responses or no response. A small spot in the excitatory
center of the field elicits only a weak excitatory response (a). A small spot in the inhibitory areaelicits a weak inhibitory response (b). Diffuse light produces no response (c).
3. By using spots of light, the excitatory or "on" areas (+) and inhibitory or "off" areas (-) can bemapped. The map of the responses reveals an elongated "on" area and a surrounding "off"area, consistent with the optimal response of the cell to a vertical bar of light.