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■ GABAergic * Cholinergic

Figure 2.1 Widely distributed networks involved in the control of saccadic eye movements in the brain. BS: brainstem; CB: cerebellum; Cd: caudate nucleus; dSC: deep layer of the superior colliculus; FEF: frontal eye field; LGN: lateral geniculate nucleus; LIP: lateral intraparietal sulcus; MNs: motor neurons; PPTN: pedunculopontine tegmental nucleus; SC: superior colliculus; sSC: superficial layers of the superior colliculus; SEF: supplementary eye field; SNr: substantia nigrapars reticulata; V1: primary visual cortex; + at the arrowhead in (b) indicates glutamatergic excitatory connection; - indicates GABAergic inhibitory connection; ACh indicates cholinergic transmission.

■ GABAergic * Cholinergic

Figure 2.1 Widely distributed networks involved in the control of saccadic eye movements in the brain. BS: brainstem; CB: cerebellum; Cd: caudate nucleus; dSC: deep layer of the superior colliculus; FEF: frontal eye field; LGN: lateral geniculate nucleus; LIP: lateral intraparietal sulcus; MNs: motor neurons; PPTN: pedunculopontine tegmental nucleus; SC: superior colliculus; sSC: superficial layers of the superior colliculus; SEF: supplementary eye field; SNr: substantia nigrapars reticulata; V1: primary visual cortex; + at the arrowhead in (b) indicates glutamatergic excitatory connection; - indicates GABAergic inhibitory connection; ACh indicates cholinergic transmission.

controlling saccadic eye movements is distributed over many brain regions, including several lobes in the cerebral cortex, cerebellum, thalamus, basal ganglia, and widespread regions of brainstem (Figure 2.1). Progress is being made by removing brain regions containing critical components of the distributed network and studying, in vitro, the biophysical properties of morphological classes of neurons and the interactions between cells residing in different parts of local microcircuits. Hypotheses about the design principles of local microcircuits must be tested by putting the local circuit back into the in vivo system (not literally, of course) and testing the effects of microinjections of pharmacological agents or by using transgenic or knock-out animals. In contrast to rhythmical motor systems, in which the temporal pattern of a local microcircuit can be monitored while performing manipulations that have effects at cellular and molecular levels, cellular and molecular levels of explanation of episodic movements must be obtained by combining information from in vivo and in vitro experimental preparations. In this chapter, we present examples of this indirect approach. The in vitro data were acquired from experiments using slice preparations to study the intrinsic circuitry and biophysical properties of neurons in the superior colliculus (SC), a brain area critically involved in the initiation and execution of saccadic eye movements.

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