Abstract

Cholinergic projections as EEG activator

Basal forebrain as activation-mediator

Non-essential role of the thalamus

Non-cholinergic EEG activation

References

Discussion
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Neurons in the basal forebrain provide the extensive cholinergic innervation of the cerebral cortex of mammals. Evidence suggests that excitation of these cells and the resulting intracortical release of acetylcholine (ACh) blocks low frequency membrane oscillations and inhibitory after-hyperpolarization in cortical pyramidal cells, resulting in the appearance of activated, desynchronized electrocorticographic activity. Thus, the cholinergic basal forebrain-cortical projection system produces activation by a direct, local action in cortex. In addition to ACh, many other brain systems are thought to play important roles in cortical activation (e.g., thalamus, brainstem, amygdala, noradrenaline, dopamine, histamine). Rather than by a direct action on cortical neurons, however, these systems modulate activation largely by an indirect action on cholinergic cells, thus altering the release of ACh from cortical terminals. Thus, in addition to its direct activating functions, the cholinergic-cortical projection system also acts as a ŒŒfinal common pathway11 through which other brain systems affect activation indirectly. To date, only one pathway has been identified that can maintain activation independent of cholinergic projections: serotonergic cortical afferents originating in the midbrain raphe nuclei produce cortical activation even after cholinergic cortical inputs have been eliminated pharmacologically or by lesioning the basal forebrain region.

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Presentation Number SAdringenberg0136
Keywords: Acetylcholine, EEG Activation, Cortex Neurons, Basal Forebrain, Serotonin