Areas of interest
What does inhibition do?*
Inhibition, learning and the body
Some of our thoughts
Nine functions of inhibition - schematic diagrams
Problems of inhibition
|* This section includes some quite technical descriptions. If that’s not how you learn best just scan or even skip the quotations in this section. Trust us, they will make more sense on a second or third reading. :o)|
SocialOur language, and in particular metaphor, makes it very easy for the mind to slip between these levels without noticing. The concept of ‘inhibition’ seems to particularly lend itself to a sloppy kind of ‘mixing of levels’. The result can be creative but it can also lead to muddled thinking, and to the unwitting extension of research way beyond its remit.
Neurons adjust or reweight their connections by strengthening or weakening them. Neuron reconnect by creating and eliminating synapses, and they rewire by growing and retracting branches. Finally, entirely new neurons are created and existing one eliminated, through regeneration.Neuronal inhibition can occur at multiple levels: with a single neuron; with a local neural cluster; and with a widely distributed network of neurons.
The most basic form of activation in the brain is excitation. ... But not all of the reciprocal influences in the brain are of this excitatory type. Many are inhibitory; they make their downstream neighbours not more, but less likely to become active, and thus they become effectively muzzled or suppressed. Being able to deploy patterns of inhibition as well as excitation confers on the human brain a good deal of its recent evolutionary power.
Why is inhibition so useful? In general, because it acts like the brake on a car. If you have a brake as well as an accelerator, you have much finer control over your speed and your steering. If the brain can inhibit as well as excite, it has much finer control over both the spreading and the sequencing of its own activation. Rather than activation just spreading out across the brain, like a blob of ink on a piece of blotting paper, it can be corralled and channelled much more precisely.
The importance of inhibition has been recognised for nearly 150 years. In 1863 the Russian physiologist Ivan Sechenov discovered that the stimulation of certain regions of a frog's brain could override reflexes that were normally involuntary, and he linked this to the human ability to inhibit our own movements, as when we 'suffer in silence' at the dentist. He observed that inhibition also gave rise to greater motor control – 'one finger can be moved separately only if the movement of the other fingers is inhibited' – and that the balance of activation and inhibition thus vastly increased the range and precision of all kinds of physical skill. 'Releasing forces acting on the brain from moment to moment shut out from activity whole regions of the nervous system, as they conversely call other vast regions into play', Sechenov observed.
But he went further than this, and argued that it was inhibition that enables the brain to decouple 'thinking' from 'action', and thus allow us to muse, meditate and consider options free of the natural tendency to transform fear or desire immediately into behaviour. 'What, actually, is the process of thinking?' he asked. 'It is the series of interconnected notions and concepts which exists in man's consciousness at a given time, and which is not expressed in external manifestations.' Sechenov's contemporary, the British neurologist David Ferrier, spotted a further implication. In 1876 he concluded: 'By checking the tendency to outward diffusion in actual motion, we thereby increase the internal diffusion, and concentrate consciousness. For the degree of consciousness is inversely proportional to the amount of external diffusion in action.' In other words, if the natural outflow of activation is dammed, it can build up behind the dam, creating stiller pools in which more conscious kind of fish may begin to breed.
Action, dampened, becomes the internalised, mental rehearsal of action, while perception, dampened, becomes the internal visualising, hearing and feeling that are the embodiments of imagination. ... Inhibition is capable of editing and distorting how unconscious brain activity gives rise to consciousness, without necessarily dampening or damming the flow of activation in the brain itself. Excitation and inhibition do not just cancel each other out, like adding '+4' and '-4' and getting zero.Ian McGhilcrist uses the same brakes on a car metaphor as Claxton to further warn us: (pp. 17-18)
Inhibition is not a straightforward concept. Inhibition at the neurophysiological level does not necessarily equate with inhibition at the functional level, any more than letting your foot off the brake pedal causes the car to halt: neural inhibition may set in train a sequence of activity, so that the net result is functionally permissive.And McGhilcrist calls upon his own historical hero: (p. 9)
The great physiologist, Sir Charles Sherrington, observed a hundred years ago that one of the basic principles of sensorimotor control is what he called 'opponent processors'. I agree with Marcel Kinsbourne that the brain is, in one sense, a system of opponent processors. In other words, it contains mutually opposed elements whose contrary influence make possible finely calibrated responses to complex situations. Kinsbourne points to three such oppositional pairings within the brain that are likely to be of significance. These could be loosely described as
'up/down' (the inhibiting effect of the cortex on the more basic automatic responses of the subcortical regions),McGhilcrist uses a 'front/back' example of “paired opponent processors” to explain how the role of inhibition is more subtle that often presupposed, enabling a fine-grained modulation of response: (pp. 91-92)
'front/back' (the inhibiting effects of the frontal lobes on the posterior cortex) and
'right/left' (the influence of the two hemispheres on one another).
The relationship of the frontal lobes, the most highly evolved and most distinctively human of all regions of the brain, with the processes going on elsewhere in the brain, including the posterior cortex, which they exist to exert control over. The frontal lobes achieve what they achieve largely through what is normally described as inhibition of the posterior part of the same hemisphere. It might be better described, however, especially in the case of the right hemisphere as modulation – the inhibitory effect is 'significantly more pronounced' in the case of the left hemisphere, perhaps in keeping with its less integrated, more black and white, style.
What do I mean by modulation? A process that resists, but does not negate. It is best thought of as the imposition of necessary distance, or delay, enabling something new to come forward. In this way it is like the apparently antagonistic relationship of the two hemispheres: it is neither that the products of one hemisphere negate the products of the other, nor that in some bland sense they merely 'complement' one another. Their incompatibility permits instead, in a dialectical synthesis, something new to arise. To take an example: if the right hemisphere's immediacy of association with emotion and the body leads it to prioritise what is close, what is 'mine', the right frontal lobe brings distance and delay to espousing 'my' position. As a result it enables others to stand forth as individual's like 'me'; it enables a broader empathy and the beginnings of altruism. This is not a negation of something by the frontal lobe, but a modulation of it, an 'unpacking', if you like, of something that was there all along, albeit in germ only – something that comes to life only when a degree of necessary distance is interposed.Claxton gives more historical background:
David Ferrier also foresaw what present-day neuroscience has confirmed: that the degree of inhibition, and the benefits that it bestows, develop throughout childhood. ... Ferrier was one of the first to localise this power of inhibition in the frontal lobes – the part of the brain that is massively developed in human beings as compared with any other animal. He observed, for example, that injury to the frontal lobes does not lead to any obvious impairment of skill. However, the consequent loss of fine inhibitory control 'causes a form of mental degradation, which may be reduced in ultimate analysis to loss of the faculty of attention'. Focussed attention relies upon inhibition, for it involves prioritising and excluding, saying 'Not now!' to competing needs and stimulation. Without that ability, a person falls prey to all kinds of distractions, and in particular, their longer-term goals and deeper values may never surface, being constantly drowned out by the incessant clamour of more immediate calls on attention. ...McGhilcrist hones in on another area of the brain, the corpus callosum, the broad band of nerve fibers joining the two hemispheres: (pp. 17-18)
Excitation and inhibition may spread at different rates. First, quick, rather indiscriminate waves of excitation ripple out from the epicentres that have been activated by the senses; and then, as their significance is weighed up, the duller ones get suppressed until a central core remains. And if this is then strong or significant enough to become conscious, a general wave of inhibition goes out to 'clean the blackboard' of all the accumulated provisional jottings and impressions, so that the next event can be inscribed on a background of relevant, as opposed to irrelevant detail. ...
So inhibition is used not only to dam the outflow of the brain; it is also employed to accentuate, or attenuate, areas of its own internal workings. But it does not do so 'mindlessly' or mechanically. Where and how fast it does depends on what the brain as a whole is up to. It also depends, ... on whose brain it is. In unpicking some of the clever ways in which the frontal lobes of the brain control the use of inhibition, we can begin to see how some of the conundrums of the unconscious may be accounted for in a new kind of way: not in terms of a mysterious sub-compartment of the mind, or a ghost in the machine, but as reflections of the brain's intrinsic – but unconscious – inhibitory intelligence.
The corpus callosum contains an estimated 300-800 million fibers connecting topologically similar areas in either hemisphere. Yet only two percent of cortical neurones are connected by this tract. What is more, the main purpose of a large number of these connections is actually to inhibit – in other words to stop the other hemisphere interfering. ... Even the excitatory fibers often terminate on intermediary neurones, or 'interneurones', whose function is inhibitory.Let’s jump several levels from neurological process to behavioural problems - sometimes, Claxton says, inhibition can “go wrong”: (pp. 271-277)
The evidence is that the primary effect of callosal transmission is to produce functional inhibition. So much is this the case that a number of neuroscientists have proposed that the whole point of the corpus callosum is to allow one hemisphere to inhibit the other. Simulation of neurones in one hemisphere commonly results in an initial brief excitatory response, followed by a prolonged inhibitory arousal in the other, contralateral, hemisphere. Such inhibition can be widespread, and can be seen on imaging.
Like the brakes on a car, inhibition makes possible greater control – but only if used appropriately. ... Behavioural inhibition can go wrong when it is either over- or under-used. ... People who suffer from Tourette's Syndrome, in which they are unable to stop themselves blurting out all kinds of socially inappropriate thoughts and feelings, are bedeviled by an inability to inhibit themselves. On the other hand, over-inhibition can be equally troublesome. Children who have not yet mastered the art of selective inhibition may overdo it, in the midst of a temper tantrum, and get locked into a kind of physical paralysis – which would be called catatonia, if they were adult schizophrenics – that can result in complete bodily rigidity, and perhaps the inability even to breathe (giving rise to what used to be called a 'blue fit'). ...McGhilcrist adds his own example: (p. 90)
When inhibition is lax or unstable, it becomes impossible to maintain concentration, and perception becomes scattered and diffuse. When both attention and behaviour are uncontrollable, as occurs with some children, the resulting syndrome is commonly referred to as 'attention deficit and hyperactivity disorder', ADHD. It is important to remember, in this context, that what we are seeing may be a loss of flexibility of control, leading to inappropriate ways of attending, rather than a biochemically caused 'inability'. ... Though the mechanism that underlies some children's scattiness involves a lack of neural inhibition, this does not mean that their brains need fixing with a sedative. Perhaps ... the fault lies in the learned triggering of disinhibition, rather than the basic consistency of their brains' chemical soup.
In the phenomenon known as 'perceptual defense', when [research subjects] have to detect words flashed very briefly, many people require an exposure three times as long to 'see' a taboo word as they do to detect a neutral one. The idea of cortical inhibition shows us how this self-protective trick can be accomplished. The word is recognised unconsciously, as a result of which the brain instantly deploys a corollary pattern of inhibition that effectively raises the threshold for consciousness. It damps its own activity, and thus prevents certain experiences from rising above the horizon of the unconscious.
Perceptual disinhibition may also account for some of the more unusual forms of human experience: ... Compelling auditory hallucinations, for example ... [are] much much more likely to occur under conditions of stress, where the inhibitory resources of the brain may be stretched to the limit. ... At the end of one's tether, there may simply be insufficient inhibition to go around, and some of the brain functions – such as imagination – that normally consume a portion of this resource may find themselves operating without the expected 'braking'. At the same time, there may also be a build-up in ... adrenalin and other stress-released hormones. As these find their way to the frontal lobes, so some of the normal functioning of the brain may be modulated or compromised: in particular, the flexible control of inhibition. ...
'Environmental dependency' syndrome refers to an inability to inhibit automatic responses to environmental cues. Individuals displaying such behaviour will, for example, pick up a pair of glasses that are not their own and put them on, just because they are lying on the table, involuntarily pick up a pen and paper and start writing, or passively copy the behaviour of the examiner without being asked to, even picking up a stethoscope and pretending to use it.Claxton concludes by returning to where he started: (pp. 296-7)
To go back to my original analogy, [excitation and inhibition] function like accelerator and brake in a car. Both can be 'full on' at the same time, and when they are, the resultant strain may risk shaking the vehicle to pieces. That, presumably, is why repression is not, after all, an entirely benign method of self-protection. Habitual repressors, people who exert high degrees of inhibitory control over their conscious experience, show exaggerated physical responses to alarming events, and are more likely to suffer from a variety of physical complaints, including hypertension and cancer. Having surveyed the literature for the prestigious Psychological Bulletin, Drew Westen concludes that 'inhibiting conscious access to one's emotions places the body, particularly the heart and the immune system, under considerable stress'. ...And lastly, lets take a look at creativity. Claxton says: (pp. 260-269)
[When] inhibition does not switch off the activation of troublesome areas of the brain, or the 'magnetic fields' of unconscious desire that keep drawing activation towards them, it sets up counter-fields, and thus creates complex cross-currents in the brain that may lead to unpredictable and unstable resolutions.
There are many interesting and puzzling aspects to creativity, of which I shall [mention] just two: how it is that creative ideas so often just pop into our minds 'out of the blue'; and why is it that some people are more creative than others? Research by Colin Martindale, at the University of Maine, suggests that variations in the inhibitory activity of the brain can account for both [kinds of creativity]. ...Inhibition, learning and the body
The thinking behind the experiment was this. Creativity consists of both inspiration and elaboration phases, but the kind of thinking that each requires is different. When looking for inspiration, people need to let the excitation of their brains preponderate over inhibition, so that a variety of ideas can be concurrently active, and their ripples can spread out more widely, overlap and thus bring to light new connections. You want to encourage a state of mind which is not the 'winner takes all' mode of focussed, purposeful attention, but one which delays foreclosure, and permits wider exploration of a priori less likely – i.e. less stereotyped or conventional – associations. ... This kind of low-inhibition brain activity shows up on the EEG as what are called 'alpha waves'.
When you move into the elaboration phase of creativity, however, you want your brain to behave differently. You want it to be more selective, critical and purposeful. In other words, you now want to deploy more inhibition, to suppress ideas other than the one you are working up, and to keep your thought processes more in order and on track. You want the centre of activation to be corralled by an inhibitory stockade that stops it leaking away. This kind of thinking shows up on the EEG as 'beta waves'.
[Experiments by Martindale showed that for the inspiration phase especially creative people] showed a dramatic switch from beta to alpha. Their frontal lobes were exerting much less inhibitory control, so that the process of reverie could take its course, and come up with some novel connections. They weren't 'figuring', they were daydreaming.
Willpower is necessary only where ability to do is lacking. Learning, as I see it, is not the training of willpower but the acquisition of the skill to inhibit parasitic action and the ability to direct clear motivations as a result of self-knowledge. (p. xi)Humberto Maturana and Pille Bunnell  point out an apparent paradox of learning. Neurobiologically, every movement is being inhibited as it occurs, and yet how do we learn to improve when attending to what we do inhibits what we do?:
If we try to learn any new skill, we find our muscles enacting not only the projected act, but also much else that is unnecessary and often contradictory to the motivated action.
Learning to inhibit unwanted contractions of muscles that function without, or in spite of, our will, is the main task in coordinating action. We have to learn to inhibit those cells of the motor cortex to which the excitation spreads. Before we become able to excite a precise pattern of cells in the wanted order, the neighboring cells all along the pattern of the cells essential to the movement become active. After adequate apprenticeship, when proficiency is achieved, only those cells that command the muscles for the desired performance send out impulses. All the others are inhibited. Without this inhibition, no coordinated action is possible.
The sensation of difficulty or resistance to action is indirectly due to the imperfect inhibition of the cells commanding the antagonistic muscles that are indispensable in forming the desired pattern. Most of the time it is not the simple inability to inhibit the parasitic contractions that is the problem, but the attempt to simultaneously enact mutually exclusive patterns ... Correct coordinated action seems, and feels, effortless no matter how great the actual amount of work involved may be. (pp. 85-86)
The nervous system is a network of neuronal elements, which operates on excitations and inhibitions. Every movement we make entails excitations and inhibitions. In the most simple way, if I contract a muscle, other muscles (the antagonists) are inhibited. Further, there is inhibition within the process of contraction of any given muscle. The point is that this play between excitation and inhibition happens in every movement: Every movement is being inhibited as it occurs. This is why, if you are learning karate and you want to break a brick, you have to aim below the brick. If you aim at the brick, the force of the blow will be diminished because inhibition takes place before the intended movement is completed.Some of our thoughts
The coordination of excitation and inhibition is involved in all neuronal activities, including what we call thinking. It is in our neurobiology that attention on what we do inhibits what we do. This is why learning a task involves relaxation—not in terms of becoming limp or falling asleep but in terms of relaxing your attention, your intent of controlling what you are doing.
an inhibitor [A]When the wider system or a longer time frame is taken into account, feedback is also involved (which itself can be inhibited):
an inhibited [B]
a means of inhibiting [➞]
Before - predicted effect of inhibition
During - in real time (requires sufficient and timely feedback)
After - reflection on actual effect of inhibition.
Too little (not enough)
Not sensitive (responsive) enough
|Function||Inappropriate type (of inhibition)|
Under-generalised (not enough pattern)
Too few examples
Over-generalised (spurious pattern)
||Inappropriate time and place|
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