Tillier; Calgary Alberta; Update: 2013-2017
Solms (2000) believes that the neuroimaging findings are generally very consistent with his neuropsychological findings, but doubts that the REM generator is a necessary part of the neural substrate for dreaming. Instead, he argues that dreaming is generated by the dopaminergic system that has its origins in dopaminergic cells in the ventral tegmentum, just above the pons, and then fans out to the amygdala, anterior cingulate gyrus, and frontal cortex. He agrees that the cholinergic pathways originating in the pons are the most frequent instigators of the necessary level of forebrain activation, but asserts that dreaming occurs "only if and when the initial activation stage engages the dopaminergic circuits of the ventromesial forebrain" (Solms, 2000, p. 849). Activation-synthesis theorists, on the other hand, see the neuroimaging results as strong support for their emphasis on the brainstem generator, while at the same time welcoming the insights into the forebrain network provided by both the neuroimaging and neuropsychological findings (Hobson et al., 2000a; Hobson et al., 2000b).
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We now update the Activation-Synthesis concept as follows: 1) high levels of cortical activation (high values of "A") are a correlate of the mind's ability to access and manipulate significant amounts of stored information from the brain during dream synthesis; 2) the blockade of external sensory input and its functional replacement by internally generated REM sleep events such as PGO waves (internal sources of "I") provide the specific activation of sensory and affective centers which prime the cortex for dream construction; and 3) the shift of the brain from aminergic to cholinergic neuromodulation (low ratios of aminergic to cholinergic neuromodulation, "M") alters the mnemonic capacity of the brain-mind and reduces the reliability of cortical circuits, increasing the likelihood of bizarre temporal sequences and associations which are uncritically accepted as waking reality when we are dreaming.
These slightly different perspectives share in common the idea that the association cortices, paralimbic structures, and limbic structures may operate as a closed loop to generate the process of dreaming. This is the starting point for the neurocognitive model proposed in this book. On the one hand, this subsystem is cut off from the primary sensory cortices that provide information about the external world, and on the other from the prefrontal cortices that integrate incoming sensory information with memory and emotion in the process of decision-making (cf. Braun et al., 1998, p. 94). This model implies that an unconstrained and freewheeling conceptual system can operate when there is sufficient activation. Its relative isolation may account for the "single-mindedness" of dreams, that is, the lack of parallel thoughts and reflective awareness (Rechtschaffen, 1978; Rechtschaffen, 1997). At the same time, as evidence presented throughout this book shows, the neural network for dreaming contains enough cognitive processing areas, such as the medial frontal cortex and anterior cingulate cortex, and perhaps the orbital-frontal cortex, to produce coherent dramatizations that often portray the dreamer's conceptions and concerns in waking life (Foulkes, 1985, pp. 209-213; Hall, 1953b). This emphasis on conceptions and concerns, based on inferences from detailed studies of dream content, provides the cognitive dimension that is lacking in activation-synthesis theory.