Neural activity in nigrostriatal circuits can signal action value and action sequence
The basal ganglia are known to be involved in the initiation of complex actions which often are composed of a sequence of movements, and for the establishment of the relation between complex actions and specific outcomes during instrumental conditioning. We established a behavioral paradigm to study the relationships between action sequences and appetitive outcomes in mice. Animals were trained to press levers for a sucrose solution as reward on a fixed-ratio schedule (FR8 - 8 presses deliver a reward). Every day animals had two single-lever training sessions, and in each of the sessions a different lever was paired with a different reward magnitude (large or small). The order of the sessions was counterbalanced. After six days of regular training, animals were given a test in extinction with both levers present to examine choice. Subsequently, the lever-reward magnitude correspondence was reversed to confirm that the animal’s action choice is contingent upon the expected value of the reward. We simultaneously implanted microelectrode arrays in the dorsal striatum (both dorsomedial and dorsolateral), the substantia nigra pars compacta (SNc) and pars reticulata (SNr), and investigated the changes in neural activity while the mice performed the task. Putative cell types were clarified based on spike waveform, baseline firing rate, and drug response (e.g. quinpirole). We observed that putative dopaminergic neurons fired phasically prior to lever pressing, which was different from the well-known cue-elicited phasic increase in dopaminergic cell firing observed in Pavlovian learning. Furthermore, the magnitude of this phasic firing increase in dopaminergic neuron firing was found to be modulated by the expected value of the action. Similar modulation by the expected magnitude of the outcome was observed in putative GABAergic neurons in the substantia nigra. In striatum, putative cholinergic interneurons paused its firing during the phasic increases in dopaminergic firing and throughout the lever pressing. Interestingly, as the animals behave more repetitively under the fixed-ratio schedule with training, neural activity related to the initiation and termination of lever-press sequences emerged. Sequence initiation and termination signals were widely found among putative dopaminergic neurons, putative GABA neurons in nigra, and also putative projection neurons in striatum. Furthermore, some of these sequence-boundary selective signals were modulated by the expected value of the action sequence. These data suggest that nigrostriatal circuits can encode the expected value of actions, and may play a crucial role in forming and expressing action sequences.
Conference:
Computational and systems
neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009.
Presentation Type:
Poster Presentation
Topic:
Poster Presentations
Citation:
(2009). Neural activity in nigrostriatal circuits can signal action value and action sequence.
Front. Syst. Neurosci.
Conference Abstract:
Computational and systems
neuroscience 2009.
doi: 10.3389/conf.neuro.06.2009.03.061
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Received:
30 Jan 2009;
Published Online:
30 Jan 2009.