The Mid-Brain Decision Triangle

Still working my way slowly through Mark Solms Hidden Spring, and barely half-way through, in Chapter 6 we have the seat, source or well-spring of consciousness, signified by his title.

(We really need one good anatomical brain map on which to project so many different writers’ resources – I mentioned before – every one published seems to annotate only those specific to that writer’s topic. This Browser version of the 3D Brain App looks most useful but needs more annotation layers. Anyway ...)

Although as a “systems thinker” I’m not particularly concerned with identifying a particular physical seat, it has great value from an “archaeological” perspective – digging down through the layers of the brain – higher and lower (generally) maps to later and earlier. Very good for understanding how, why, when and in what context capabilities arose. Apart from the occasional evolutionary cul-de-sac, form does tend to follow function. As ever all empirical evidence for which elements and connections do indeed support which capabilities and functions come from normal behaviours being physically or electro-chemically interrupted in abnormal cases, with the masses of new neuro-correlate sensing now available to “see” what is happening, where and when.

(Any complex topic has at least one time axis – in real-time-living, individual-lifecycle-development and/or species-evolution time-scales. It was Foucault who first introduced me to the archaeological aspect of knowledge and Jorn Barger, the original blogger, who turned me on to timeline representations. But again I digress.)

Without getting philosophical or overly definitive about exactly what we mean by our consciousness or the volition to act according to our will, Solms with ample acknowledgement to Panksepp and Merker, thoroughly emphasises the feeling or affective subjective qualities in play. (As I said in the previous post – any “science” discounting these is cutting itself off from ever explaining consciousness or will satisfactorily. This is surely a given, but one nevertheless denied by so many orthodox scientists and scientific philosophers – and thus almost all popular scientist personalities)

Although Solms is circumspect in not overclaiming – at this stage half-way through his book – he really has also shown that the “qualia” half of the so-called hard problem is a non-event. Consciousness is all about subjective experience. (How hard can it be?)

In looking at “levels” of consciousness from comatose (or actually dead) to  maximally conscious (heightened engagement or mindful flow, say) he is at pains to notice more than one axis of wakefulness / awareness and attention / engagement, the latter he unapologetically dubs “arousal”. There are both scope and kind axes in the subject of consciousness. (In fact he has an appendix on this which “aroused” my interest enough to read first when I originally skimmed the book. I didn’t just “notice” it, I was motivated enough to engage in checking out that one small piece as part of my “decision-to-read” process.)

Anyway, not surprisingly our source of consciousness is a sub-system of the whole – the mid-brain decision triangle – where knowledge and affect are constantly compared and updated.

How do I feel about what I know and
what, if anything, should I do about it?

A sub-system evolved in all vertebrates, not just we humans, despite our massively developed cortex.

Para-phrase quotations of Ch6 The Source:

(Note two things. This is a massive spoiler in terms of copyright content, acknowledged, but also a massive risk of misrepresentation in the paraphrasing and in introducing my own / McGilchrist thoughts, also acknowledged. In paraphrase I’ve obviously left out many of Solms own qualifications and caveats. I’ve also kept in lots of technical specifics which I probably don’t understand as Solms intended, primarily to allow me later checking against other resources.)

Most people with even a casual interest in the brain … have heard of chemical neuro-transmitters involved in individual synaptic – fire/not-fire – communications between neurons.

Fewer are aware of post-synaptic-modulation involving chemical neuro-modulators which more diffusely modulate the progress of signals – speed and intensity – in whole populations or bundles of neurons in localised areas of the brain. It’s this “level” of signal that drives the “arousal” axis of our awareness / engagement. It’s messy, non-binary and arises endogenously from not just the “Reticular Activating System” (RAS) but also from other sub-cortical and even non-neurological bodily structures.

(Depending how and where released some of these chemicals do both.)

5 important neuromodulators in the reticular brainstem system (there are more than a hundred slow-acting hormones and peptides involved around the brain and body) are:

    • dopamine
      – (sourced mainly in ventral tegmental area and substantia nigra)
    • noradrenaline
      – (sourced mainly in locus coeruleus complex)
    • acetylcholine
      – (sourced mainly in mesopontine tegmentum and basal forebrain nuclei)
    • serotonin
      – (sourced mainly in raphe nuclei
    • histamine
      – (sourced mainly in tuberomammillary hypothalamus)

The shift from vegetative wakefulness (minimal awareness) to affective arousal (intentional engagement) is driven by neuromodulators acting on a small knot of neurons called the periaqueductal grey (PAG).

The PAG is separate from, but lies right next to and is densely interconnected with, the RAS, therefore affected by the same neuromodulators, but crucially the direction of their connectivity is reversed: The RAS influence is upwards into the cortex, the PAG only receives communications downwards from the cortex.

Immediately adjacent (behind) the PAG is the multi-layered superior colliculi (SC). Its layers provide mappings of the body in terms of motor maps and spatio-sensory aspects, together they assemble a massively compressed and integrated representation of the exteroceptive world, arriving both from the cortex and from sub-cortical sensory-motor regions.

The PAG is the centre for balancing, prioritising or segueing “needs” data according to its salience, orchestrating different coping strategies in response to sensory inputs. All affective circuits converge on the PAG.

The SC represents the moment by moment state of the objective (LH-cortex-modelled) sensory and motor body, in much the same way as the PAG monitors its subjective (RH-cortex-felt) need state. This affective / sensory / motor interface between the PAG, the SC and the mid-brain locomotor region is the “mid-brain decision triangle” (Merker); the primal self, the very source of our sentient being (Panksepp).

The deepest layer of the SC is a map (model) that controls eye movements – one that is intrinsically more stable than the other layers, since these others are calibrated against it, thereby establishing the unified “point of view” that characterises our perceptual experience, even though our actual eye movements are constantly flitting about the “scene”. “… a fully articulated panoramic 3D world composed of shaped, solid objects, the world of our familiar phenomenal experience” (Merker). This scene is our constructed view of reality which also explains why we experience ourselves as living in our heads.

Our here and now perceptions are constantly guided by predictions, generated (modelled) from our long-term memory. That is why far fewer neurons propagate signals from the sense organs to the internal sub-systems than the other way. The heavy lifting is done by the predictive signals that meet the sensory ones arriving from the periphery. We do not rebuild our whole world model constantly from the sensory inputs, thus saving enormous information processing / metabolic effort.

(Note the caveats at the start of that long paraphrase / quote.)

For me that all sounds entirely believable, however verifiable Solms claims and interpretations, which I may anyway have misinterpreted. I’ve subscribed to a Permissive Supervisory Control System view of the brain-mind for as long as I’ve taken any interest in it. A mix of feed-forward as well as feed-back with the vast majority of information and processes at autonomous “sub-conscious” levels for efficiency (attention) and tractability (effectiveness) reasons. Free will being just the right amount of free-won’t.

And my interest – in psycho-cybernetics – has always been about how we individually and collectively make and enact good decisions.


PS My other interest at the metaphysical limits of physics is information itself as the complement of entropy (after Boltzmann) at the most fundamental level of physics.  The technical appendix on arousal – mentioned above – was actually entitled “Arousal and Information” referenced in the final sentence of this Chapter 6 as a “bridge” to the next. Chapter 7 is “The Free Energy Principle” – hopefully the “plus” in homeostasis-plus. We shall see Eddo?

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: