Chapter

Space,Time and Memory in the Hippocampal Formation

pp 153-189

Date:

Modulatory Influences on the Hippocampus and Entorhinal Cortex

  • Kishan GuptaAffiliated withCenter for Memory and Brain, Department of Psychology, Graduate Program for Neuroscience, Boston University
  • , Michael E. HasselmoAffiliated withCenter for Memory and Brain, Department of Psychology, Graduate Program for Neuroscience, Boston University Email author 

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Abstract

The functional regulation of cortical circuits depends on neuromodulators such as acetylcholine, norepinephrine, serotonin, and dopamine to alter the information processing mediated by fast transmitters such as glutamate and GABA. The primary mechanisms shared by the neuromodulators include altering the dynamics of excitatory and inhibitory synaptic transmission, altering synaptic modification properties, and changing the resting membrane potential. Aside from synaptic modulation, the same neuromodulators can also affect spike frequency with prominent examples including pyramidal cell spike frequency adaptation. Though the cellular effects of neuromodulators may be similar, a diversity of upstream systems regulates the influence of competing neuromodulators both in the spatial distribution and temporal dynamics of release. The diversity of neuromodulator receptor subtypes also influences the nature of the cellular effects of neuromodulation. The purpose of this chapter is not to differentiate between competing neuromodulatory systems, but to survey evidence for how different neuromodulators affect change in information transmission in the hippocampal system. This chapter also highlights physiological examples of acetylcholine effects in active research areas of entorhinal persistent spiking, subthreshold properties of stellate cells, and theta modulation of hippocampal and entorhinal networks.