Prefrontal synthesis (PFS, also known as Mental Synthesis) is the conscious purposeful process of synthesizing novel mental images. PFS is neurologically different from the other types of imagination, such as simple memory recall and dreaming. Unlike dreaming, which is spontaneous and not controlled by the prefrontal cortex (PFC), PFS is controlled by and completely dependent on the intact lateral prefrontal cortex. Unlike simple memory recall that involves activation of a single neuronal ensemble (NE) encoded at some point in the past, PFS involves active combination of two or more object-encoding neuronal ensembles (objectNE). The mechanism of PFS is hypothesized to involve synchronization of several independent objectNEs. When objectNEs fire out-of-sync, the objects are perceived one at a time. However, once those objectNEs are time-shifted by the lateral PFC to fire in-phase with each other, they are consciously experienced as one unified object or scene.
History of the term
The earliest reference to mental synthesis is found in the doctoral dissertation of SJ Rowton written in 1864. Paraphrasing Cicero’s description of nature that can only be unified in someone’s mind, SJ Rowton writes: “... there cannot be one thing unless by a mental synthesis of many things or parts ...”
In the 20th century the term mental synthesis was often used in psychology to describe the experiments of combinatorial nature. In a common experimental setup, subjects are instructed to mentally assemble the verbally described shapes in various ways. For example, the shapes may have been the capital letters ‘J’ and ‘D’, and the subject would then be asked to combine them into as many objects as possible, with size being flexible. A suitable answer in this example would be: an umbrella. The performance in this task is then quantified by counting the number of legitimate patterns that participants construct using the presented shapes.
As the neurobiological study of imagination advanced in the 21st century, there was a need to distinguish the neurologically distinct components of imagination: first in terms of their dependence on the lateral PFC and second in terms of the number of involved neuronal ensembles. As a result, “mental synthesis” was adapted to describe the active process of assembling two or more independent objectNEs from memory into novel combinations. The term "prefrontal synthesis" was later proposed for use in place of "mental synthesis" in order to emphasize the role of the PFC and further distance this type of voluntary imagination from other types of involuntary imagination, such as REM-sleep dreaming, day-time dreaming, hallucination, and spontaneous insight.
There is evidence that a deficit in PFS in humans presents as language which is "impoverished and show[s] an apparent diminution of the capacity to 'prepositionize'. The length and complexity of sentences are reduced. There is a dearth of dependent clauses and, more generally, an underutilization of what Chomsky characterizes as the potential for recursiveness of language"
Neuroscience of prefrontal synthesis
The mechanism of PFS is hypothesized to involve synchronization of several independent object-encoding neuronal ensembles (objectNEs). When objectNEs fire out-of-sync, the objects are perceived one at a time. However, once those objectNEs are time-shifted by the lateral prefrontal cortex (LPFC) to fire in-phase with each other, they are consciously experienced as one unified object or scene. The synchronization hypothesis has never been directly tested but is indirectly supported by several lines of experimental evidence. Furthermore, it is the most parsimonious way to explain the formation of new imaginary memories since the same mechanism of Hebbian learning (“neurons that fire together wire together”) that is responsible for externally-driven sensory memories of objects and scenes can be also responsible for memorizing internally-constructed novel images, such as plans and engineering designs. In the process of formation of novel receptive memories, neurons are synchronized by simultaneous external stimulation (e.g., light reflected from a moving object is falling on the retina at the same time). In the process of formation of novel imaginary memories, neurons are synchronized by the LPFC during waking or spontaneously during dreaming. In both cases it is the synchronous firing of neurons that wires them together into new stable objectNEs that can later be consolidated into long-term memory.
- Braun, A. (1 July 1997). "Regional cerebral blood flow throughout the sleep-wake cycle. An H2(15)O PET study". Brain. 120 (7): 1173–1197. doi:10.1093/brain/120.7.1173. PMID 9236630.
- Christoff, Kalina; Gabrieli, John D. E. (4 November 2013). "The frontopolar cortex and human cognition: Evidence for a rostrocaudal hierarchical organization within the human prefrontal cortex". Psychobiology. 28 (2): 168–186. doi:10.3758/BF03331976 (inactive 31 May 2021). ISSN 0889-6313.CS1 maint: DOI inactive as of May 2021 (link)
- Waltz, J. A.; Knowlton, B. J.; Holyoak, K. J.; Boone, K. B.; Mishkin, F. S.; de Menezes Santos, M.; Thomas, C. R.; Miller, B. L. (1 March 1999). "A System for Relational Reasoning in Human Prefrontal Cortex". Psychological Science. 10 (2): 119–125. doi:10.1111/1467-9280.00118. S2CID 44019775.
- Duncan, John; Burgess, Paul; Emslie, Hazel (March 1995). "Fluid intelligence after frontal lobe lesions". Neuropsychologia. 33 (3): 261–268. doi:10.1016/0028-3932(94)00124-8. PMID 7791994. S2CID 38259670.
- Luria, Aleksandr Romanovich (1980). Higher cortical functions in man (2nd ed.). New York: Basic Books. ISBN 978-0465029600.
- Fuster, Joaquín M. (2008). The prefrontal cortex (4th ed.). Amsterdam: Academic Press/Elsevier. ISBN 978-0123736444.
- Baker, S.C.; Rogers, R.D.; Owen, A.M.; Frith, C.D.; Dolan, R.J.; Frackowiak, R.S.J.; Robbins, T.W. (June 1996). "Neural systems engaged by planning: a PET study of the Tower of London task". Neuropsychologia. 34 (6): 515–526. doi:10.1016/0028-3932(95)00133-6. hdl:21.11116/0000-0001-A39D-6. PMID 8736565. S2CID 7366716.
- Vyshedskiy, Andrey; Dunn, Rita (29 December 2015). "Mental synthesis involves the synchronization of independent neuronal ensembles". Research Ideas and Outcomes. 1: e7642. doi:10.3897/rio.1.e7642.
- Rowton, Samuel James (1864). On the Inseparable Co-operation of Sense and Intellect for Arriving at Cognitions.
- Finke, Ronald A.; Slayton, Karen (May 1988). "Explorations of creative visual synthesis in mental imagery". Memory & Cognition. 16 (3): 252–257. doi:10.3758/BF03197758. PMID 3393086. S2CID 19651078.
- Pearson, David G.; Logie, Robert H.; Gilhooly, Ken J. (September 1999). "Verbal Representations and Spatial Manipulation During Mental Synthesis". European Journal of Cognitive Psychology. 11 (3): 295–314. doi:10.1080/713752317.
- Kokotovich, Vasilije; Purcell, Terry (September 2000). "Mental synthesis and creativity in design: an experimental examination". Design Studies. 21 (5): 437–449. doi:10.1016/S0142-694X(00)00017-X.
- Barquero, B.; Logie, R.H. (September 1999). "Imagery Constraints on Quantitative and Qualitative Aspects of Mental Synthesis". European Journal of Cognitive Psychology. 11 (3): 315–333. doi:10.1080/713752318.
- PEARSON, DAVID G.; LOGIE, ROBERT H. (1 January 2003). "Effects of Stimulus Modality and Working Memory Load on Mental Synthesis Performance". Imagination, Cognition and Personality. 23 (2): 183–191. doi:10.2190/KRQB-0CED-NX6J-HQ72. S2CID 146644818.
- Vyshedskiy, Andrey (2014). On the origin of the human mind (2nd ed.). [S.l.]: Createspace Indep Pub. ISBN 978-1492963615.
- Vyshedskiy, Andrey (2014). Evolution of language: proceedings of the 10th international conference. Singapore: World Scientific. pp. 344–352. ISBN 978-981-4603-62-1.
- Vyshedskiy, Andrey (2019). "Neuroscience of imagination and implications for human evolution". PsyArXiv. doi:10.31234/osf.io/skxwc.
- Fuster, Joaquín M. (2008). "Human Neuropsychology". The prefrontal cortex. Academic Press. pp. 171–219. doi:10.1016/B978-0-12-373644-4.00005-0. ISBN 9780123736444.
- Vyshedskiy, Andrey (20 July 2019). "Language evolutin to revolution". Research Ideas and Outcomes. doi:10.3897/rio.5.e38546.
- Hipp, Joerg F.; Engel, Andreas K.; Siegel, Markus (January 2011). "Oscillatory Synchronization in Large-Scale Cortical Networks Predicts Perception". Neuron. 69 (2): 387–396. doi:10.1016/j.neuron.2010.12.027. hdl:1721.1/92314. PMID 21262474. S2CID 7658076.
- Sehatpour, P.; Molholm, S.; Schwartz, T. H.; Mahoney, J. R.; Mehta, A. D.; Javitt, D. C.; Stanton, P. K.; Foxe, J. J. (11 March 2008). "A human intracranial study of long-range oscillatory coherence across a frontal-occipital-hippocampal brain network during visual object processing". Proceedings of the National Academy of Sciences. 105 (11): 4399–4404. Bibcode:2008PNAS..105.4399S. doi:10.1073/pnas.0708418105. PMC 2393806. PMID 18334648.
- Hirabayashi, T. (2 November 2005). "Dynamically Modulated Spike Correlation in Monkey Inferior Temporal Cortex Depending on the Feature Configuration within a Whole Object". Journal of Neuroscience. 25 (44): 10299–10307. doi:10.1523/JNEUROSCI.3036-05.2005. PMC 6725794. PMID 16267238.
- Rodriguez, Eugenio; George, Nathalie; Lachaux, Jean-Philippe; Martinerie, Jacques; Renault, Bernard; Varela, Francisco J. (February 1999). "Perception's shadow: long-distance synchronization of human brain activity". Nature. 397 (6718): 430–433. Bibcode:1999Natur.397..430R. doi:10.1038/17120. PMID 9989408. S2CID 4413866.
- Uhlhaas, Peter J.; Singer, Wolf (October 5, 2006). "Neural Synchrony in Brain Disorders: Relevance for Cognitive Dysfunctions and Pathophysiology". Neuron. 52 (1): 155–168. doi:10.1016/j.neuron.2006.09.020. PMID 17015233.
- "The neuroscience of imagination". TED-Ed.