The Conscious Brain

Author: Jesse J. Prinz, Published by Oxford University Press (2012)
Summary and review of the above book

INTRODUCTION: Prinz argues that a theory of consciousness requires a process, and also a location in the brain for that process to take effect. The direction of attention is seen as necessary and sufficient for consciousness to arise. The location is argued to be the secondary or intermediate cortex. Consciousness generated in this area is then used by the working memory for deliberative processing; this is why evolution selected for consciousness. The idea is valuable in counterbalancing an arguable over-emphasis on frontal regions in consciousness studies. Weaknesses are the conflict with evidence for consciousness in the higher rather than the secondary cortex, the lack of mention of the brain’s evaluative regions, and a failure to tackle the hard problem; for the last, we need some suggestion of how the intermediate cortex is physically different from the rest of the brain’s processing, in such a way as to produce subjective experience. For more information about Prinz please click on the following link: http://web.gc.cuny.edu/philosophy/faculty/prinz.htm

 

New style of consciousness philosophy

Prinz has moved away from the consciousness philosophy of earlier decades when theories were propounded with only passing references to current research in neuroscience. He postulates two steps for a theory of consciousness, a process for the brain to become conscious, and a place in the brain where this happens. Neural processing as such does not describe consciousness, because the greater part of neural activity is unconscious. Therefore, something extra beyond this basic processing is required.

According to Prinz’s theory, attention is the necessary and sufficient means for perceptions to come into consciousness. When we attend, perceptions come into consciousness, but otherwise they remain unconscious. Attention has been demonstrated to enhance neural activity in brain regions related to what is being attended, while neurons related to unattended stimuli are inhibited. Unattended stimuli may influence processing, but are not involved in deliberation or planning. The structures for direction of attention are thought to be located in the inferior posterior parietal, the frontal eye field and the lateral frontal region.

Location of Consciousness

Prinz locates consciousness in the secondary/intermediary sensory cortex, hence his theory is called, ‘attended intermediate-level representation’ (AIR). The extrastriate or secondary cortex is suggested as being the brain region supporting consciousness. This is the level at which discrete features are integrated into coherent representations. The secondary cortex contains structures dealing with colour, motion and form, views of objects from different vantage points, separation of objects from backgrounds, visual depth and texture.

Prinz postulates that the act of attending changes how representations are processed, and this change brings the representations into consciousness. Qualia are described as, conscious or phenomenal states, experiences and feelings, and are viewed as brain-generated, in that there is no red out there, just red generated in the brain. Moreover, no two qualia have been found to correlate to the same brain state. Different experiences relate to different brain states. Neurons that code for red need a means of distinguishing them from, neurons that code for blue.553x343x09-15_jpg_pagespeed_ic_9PtS9lHp1G

Working memory, decision-taking & cognition

Working memory involves the lateral frontal cortex. Different sense modalities are thought to involve separate working memory systems, which can retain inputs after the original stimulus has disappeared. Consciousness is suggested to occur when attention makes information available to working memory via the secondary cortex. The selection of consciousness by evolution reflects the advantage of the selective choices that working memory processing allows, plus foreseeing the outcomes of possible behaviours. Prinz views consciousness as useful for decision-taking, rather than motor actions. Consciousness involves sensory brain areas, rather than cognition. Thoughts and concepts derive from perceptions. Thoughts are connected to sensory perceptions, and cognition can be reduced to sensory inputs. Prinz sees thoughts as conscious, but only because they relate to the sensory. Concepts derive from sensory records in the memory system.

Neuroscience supports aspects of AIR theory. It is plausible that attention is a necessary trigger for consciousness. There is evidence for the sensory cortex being independently conscious rather than merely a dependency of the frontal brain (Cahart-Harris et al, 2011), (Malach, 2007, 2006) (Goldberg, 2006). Dream sleep is also known to involve deactivation of parts of the frontal cortex, while sensory areas are highly activated. The argument for the evolutionary usefulness of consciousness is also consistent with research on the neural processing of decisions.

Criticism of AIR theory

However, there are weaknesses in AIR. The claim that consciousness is generated only in the secondary sensory cortex, and not at all in the higher sensory cortex, goes against evidence for visual perceptions involving neurons in the medial temporal lobe that get projections from the last stage of visual processing in the inferior temporal region (Quiroga, 2008, 2008, 2007), (Ogman & Breitmeyer, 2006), (Kreiman, 2002). Similarly, the attempt to argue against the evidence of TMS is hard to square with research in which TMS removes consciousness (Ogmen & Breitmeyer, 2006, 2006).

Prinz views the self as the product of perceptions with no self existing beyond the fact of perceptions. Recent studies suggest the sense of self correlates to processing in superior frontal gyrus (Goldberg, 2006). He argues that this has connections to the working memory, and therefore the self must be only relevant to working memory. However, there seems no reason why, as the Goldberg study suggests, activity in this brain region should not relate adaptively to longer-term memories, and the distinctions between the body and the environment that are directly relevant to survival and development.

The weakest aspect of AIR is that it effectively ignores the brain’s evaluative/emotional processing, something that is well examined by modern studies, (Zald & Scott, 2006) (Kosiol & Budding, 2009), (Rolls, 2008, 2007), (Chang, 2013), (Wang, 2013) (Shidara, 2002). There is thus a problem with not getting a theory of the connections between the sensory/perception system, the evaluative/emotional system and the rational/planning system. In modern research, the reward/punisher evaluative system interconnects with the reasoning/planning of the dorsolateral prefrontal. The processing of dorsolateral and the evaluative orbitofrontal are merged in the basal ganglia, upstream of actions and behaviour. (Kosiol & Budding, 2009). It is possible that signals from the reward system play a part in the fronto-parietal control of attention (Sestieri, 2012).

The ‘Hard Problem’ remains

Even accepting the AIR theory in its entirety, still leaves the ‘hard problem’, as to what distinguishes the conscious intermediate sensory cortex, from the unconscious remainder of the brain. Attention enhances some neurons and inhibits others in the sensory cortex, but it is not clear how this tuning could generate an additional physical process, consciousness, not seen in the rest of the brain’s processing.

 

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