Possible functions of consciousness 2 – gate to meaning

This is the second post in a series. The first post dealt with the importance of ‘experience’ in the sense of episodic memory, with consciousness supplying the moments making up an episode. Events that we are not conscious of simply do not get stored in episodic memory.

There is another type of memory which is not episodic, not autobiographical, carries no time and place information. It is usually called the semantic memory although it is not just about language. It stores facts, the sort of facts that you can state in natural language or some other representation (equations, musical scores, diagrams etc.). These are time-less, place-less, agent-less bits of understanding. This is memory of meanings, understandings, relationships, knowledge, ideas, concepts, and words with minimal context. The storage and retrieval processes of episodic and semantic memory appear to be separate with the exception that they are both declarative, or explicit, memory systems and therefore storage is from consciousness and retrieval is into consciousness.

What is the meaning of a word? Well, a word by itself does not have meaning. Meaning is gained by the relationships between words – they are defined in terms of other words/concepts.

Meaning is gained by how an entity takes part in the model of reality that we produce, by how it relates to other entities in the model. This model is what consciousness is derived from. Consciousness, in effect, brings the meaning from the model to the semantic memory and consciousness holds the meaning when it is retrieved from memory.

It is not clear whether semantic memory is stored as networks, matrices, hierarchies, chunks or some other embodiment. Whatever the structure, it supplies us with categories, contrasts, generalizations, and metaphoric analogs. Probably this structure is shared with other mammals, perhaps other vertebrates, but language has made it a powerful tool for humans by storing words so that they are retrievable into consciousness in ways that fit with our world model.

Language and other meaning systems are so important to us in communication with others and even within ourselves – their value cannot be overstated. The function of consciousness as a gateway to semantic memory is worth a great deal of biological cost.

In the three and a half years that I have been closely following scientific ideas about consciousness on the web, I have encountered a number of excellent ways to look at/ models of/ theories about consciousness. But I have not encountered anyone make a case for an intimate link between consciousness and declarative memory (except for the obvious definition of ‘declarative’ and ‘explicit’). I am surprised at this lack because the link seems so important in my view. If any readers know of such a argument having been made, I would appreciate a link to it.

There is more to come. The posts in this series to date:

Possible functions of consciousness 1 – leading edge of memory

Losing self-awareness

The New Scientist has a article by Giai Vince (here) on research by Ilan Goldberg’s group on the lost of self awareness in some circumstances.

While people were being scanned with fMRI they were asked to make an identification of whether there was an animal on a card as it was shown. The test was done three times: slowly, quickly, and with an indication of emotional response to the card rather than the presence of an animal. The test was also done with musical clip identifying if there was a trumpet (slow and fast) and emotional reaction.

Goldberg found that when the sensory stimulus was shown slowly, and when a personal emotional response was required, the volunteers showed activity in the superfrontal gyrus – the brain region associated with self-awareness-related function.

But when the card flipping and musical sequences were rapid, there was no activity in the superfrontal gyrus, despite activity in the sensory cortex and related structures.

“The regions of the brain involved in introspection and sensory perception are completely segregated, although well connected,” says Goldberg, “and when the brain needs to divert all its resources to carry out a difficult task, the self-related cortex is inhibited.”

This seems, to my mind, a different cause for losing self-awareness then that which comes from very high levels of skill in a Zen-like activity or from some types of mediation. So we have at least three ways to lose self awareness: too busy for introspection, so skilled that thinking interferes with performance, having learned how to steer attention. Probably there are drugs that also eliminate self awareness.

An interesting old paper

An paper has surfaced on Sandygautam Cognitive Daily (thanks to @mocost tweet) called ‘Why can’t you tickle yourself?’ by Blakemore, Wolpert and Frith, published 11 years ago. (cited below). Here is the abstract:

It is well known that you cannot tickle yourself. Here, we discuss the proposal that such attenuation of self-produced tactile stimulation is due to the sensory predictions made by an internal forward model of the motor system. A forward model predicts the sensory consequences of a movement based on the motor command. When a movement is self-produced, its sensory consequences can be accurately predicted, and this prediction can be used to attenuate the sensory effects of the movement. Studies are reviewed that demonstrate that as the discrepancy between predicted and actual sensory feedback increases during self-produced tactile stimulation there is a concomitant decrease in the level of sensory attenuation and an increase in tickliness. Functional neuroimaging studies have demonstrated that this sensory attenuation might be mediated by somatosensory cortex and anterior cingulate cortex: these areas are activated less by a self-produced tactile stimulus than by the same stimulus when it is externally produced. Furthermore, evidence suggests that the cerebellum might be involved in generating the prediction of the sensory consequences of movement. Finally, recent evidence suggests that this predictive mechanism is abnormal in patients with auditory hallucinations and/or passivity experiences.

We distinguish sensations that we produced from those that happen in the environment, and this would be important to appropriate responses. We also need to monitor our actions, to be sure they produce the outcomes we planned. For these reasons, our senses need to know what motor commands are being executed and to predict what sensory information to expect.

In order to generate sensory predictions, it is postulated that the central nervous system contains a central monitor or internal `forward model’. Forward models mimic aspects of the external world and the motor system in order to capture the forward or causal relationship between actions and their outcomes.

The experiments used an imposed robotic arm between the agent producing a tickle action and the part of the body being tickled. This allowed the subject to administer stimuli to themselves that could be delayed or rotated.

The results showed that subjects rated the self-produced tactile sensation as being significantly less tickly, than an identical stimulus produced by the robot (under the experimenter’s control). Furthermore, subjects reported a progressive increase in the tickly rating as the delay was increased between 0 ms and 200 ms and as the trajectory rotation was increased between 0 and 90 degrees. These results support the hypothesis that the perceptual attenuation of self-produced tactile stimulation is due to precise sensory predictions, rather than a movement- induced non-specific attenuation of all sensory signals. When there is no delay or trajectory rotation the model correctly predicts the sensory consequences of the movement, so no sensory discrepancy ensues between the predicted and actual sensory information, and the motor command to the left hand can be used to attenuate the sensation on the right palm. As the sensory feedback deviates from the prediction of the model (by increasing the delay or trajectory rotation) the sensory discrepancy between the predicted and actual sensory feedback increases, which leads to a decrease in the amount of sensory attenuation.

Next they measured brain activity associated with the prediction and attenuation of tickling.

There were four conditions: self-generated tactile stimulation; self-generated movement without tactile stimulation; externally generated tactile stimulation; and rest. Using this design we were able to assess the difference in brain activity during self-generated relative to externally generated tactile stimulation while factoring out activity associated with self-generated movement and tactile stimulation. Analysis of the imaging data resulted in the creation of statistical parametric maps refl̄ecting the two main effects, movement and tactile stimulation, and the interaction between these two factors.

They found the secondary somatosensory cortex and the anterior cingulate gyrus had attenuated activity by the movement. In contrast, the right anterior cerebellar cortex was deactivated only by movement that resulted in stimulus and not movement alone. It was also activated by externally produced stimulation.

We suggest that the cerebellum is involved in predicting the specific sensory consequences of movements and in providing the signal that is used to attenuate the somatosensory response to self-produced tactile stimulation.

Tickling self-produced and externally produced stimulation was compared for schizophrenic patients with auditory hallucinations and/or passivity, patients without these symptoms. with match controls.

The results demonstrated that normal control subjects and patients with neither auditory hallucinations nor passivity experienced self-produced stimuli as less intense, tickly and pleasant than identical, externally produced tactile stimuli. In contrast, patients with these symptoms did not show a decrease in their perceptual ratings for tactile stimuli produced by themselves as compared to those produced by the experimenter. These results support the proposal that auditory hallucinations and passivity experiences are associated with an abnormality in the forward model mechanism that normally allows us to distinguish self-produced from externally produced sensations. It is possible that the neural system associated with this mechanism, or part of it, operates abnormally in people with such symptoms.

There it is – another bit of evidence for near-future prediction in our experience of the world.

ResearchBlogging.org

Blakemore SJ, Wolpert D, & Frith C (2000). Why can’t you tickle yourself? Neuroreport, 11 (11) PMID: 10943682

Possible functions of consciousness 1 – leading edge of memory

In evolutionary terms, why, oh why, do we pay the enormous biological cost of consciousness? Biological costs imply biological functions.

What is the cost? The human brain uses 20% of the body’s oxygen intake and 25% of its glucose demand. In the depth of anesthesia it consumes half as much, still 10-12%, a sizable part of the total energy budget. The other 50% is used for actual mental work as opposed to just maintaining life in the brain. But in ordinary conscious operation the brain uses nearly the same energy whether it is concentrating on a task or resting, the amount of work does not seem to be that important to the use of energy. Therefore, it is safe to guess that maintaining consciousness itself is an important fraction of this other 10-12% of the body’s total energy use. Let us say that in the region of 5% of the body’s energy consumption goes towards the process of consciousness. That is a high price in biological terms and would certainly be eliminated in evolutionary history if there were not an important function, or functions, being ‘paid for’.

So what is the function of consciousness? On the surface it appears to be a frill. Sleep walking shows that consciousness is not that necessary for normal activity over short periods. A person can get up from bed, get dressed, go outside, get in their car and drive it without accident and without waking or being aware. Well learned actions and responses do not need consciousness for their execution – so the important function must be more than just routine living. The reasons for consciousness are not known but there are a number of candidates, any or all might be important in explaining why we have consciousness. This is the mystery that attracted me.

This is the first of a series of posts on possible functions of consciousness.

My original idea was that consciousness was part of memory. And I remember the time in the late 70′s when that idea came to me. I thought how do I know I am conscious and the only answer I found was that I remembered what came before ‘now’. If I had no reason at the time to question the continuity of my memory then I was and had been conscious. This seemed to me a good hint that there might be a connection between consciousness and memory. There had to be a way to form a model of reality that could be the source of material for memory and, equally important, there had to be a model structure that could hold the recalled past or imagined future in the same form that is used for the present.

The way I saw it then, I wrote down a couple of years later, emphasized the importance of remembered experience to cognition and learning. Other ideas have been added later but I still associate consciousness with memory. Here is some writing from 30 years ago:

“The simplest nervous system amounts to a number of sensitive sensory neurons contacting a number of effecting motor neurons, to give a fixed set of reflex responses to environmental change. The sensory neurons notice certain changes in the environment and trigger particular motor neurons to respond to the changes. The only learning that is possible in this structure is habituation, the temporary loss of a reflex when it is triggered at a high frequency. A more flexible behavior is possible when inter-neurons are interposed between the sensory set and the motor set. With small numbers of inter-neurons, the behavior is still reflexive but the inter-neurons allow more complex and discriminating patterns of movement. A small amount of non-habituation learning is possible. Further, the inter-neuron net can also maintain spontaneous rhythms. The spinal cord and much of the lower brain stem is such a network. It generates the rhythms of heart beat, breathing and alternate limb movements; it mediates the reflexes of avoidance movements; it maintains postural muscle tone. But its ability to learn is limited.

In order to learn, in the sense of gaining from past experiences, it is necessary to have experiences, to store them and evaluate them. When inter-neurons increase in number and become organized into large sheets and nuclei, it is possible to deal in experience. The inter-

neurons function to build a coherent model of experience, store an edited version of this model as a sequential memory, simulate future events with the model and compare results with expectations. Now there is the ability to learn from experience, there is thought. It is important at this stage to point out that in this concept of thought, there is a difference between the model (and its production and use) and our consciousness of it. The phenomenon of consciousness is associated with the formation of an edited form of the model and the storage of this summary. Consciousness is not the modeling activity itself.

If we ask the question, “How do I know that I am conscious at this very instant of time?” it is difficult to answer without referring to the continuum of past, present and future experience. Our awareness of having been without consciousness is simply a discontinuity in the memory. Consciousness can be pictured as the leading edge of memory, having the same detail and structure as recent memory. It is one of the finished products of thought, not the process of thought. Far from being uniquely human, consciousness will occur in all animals with brains of the same memory fabricating type, at least the higher vertebrates. The elaborateness of the edited model would dictate the elaborateness of the consciousness of it. ”

It seems to me that the feeding of working memory and short-term memory is one of the important functions of consciousness; and, the acceptance of recalled memories and of imaginings constructed from memory fragments is another important associated function. Consciousness is the creation of experience that can be stored, retrieved and manipulated.

Prediction of smells

ScienceDaily reports on a recent paper in Neuron by Zelano, Mohanty and Gottfried, Olfactory Predictive Codes and Stimulus Templates in Piriform Cortex. (here)

In the moments before you “stop and smell the roses,” it’s likely your brain is already preparing your sensory system for that familiar floral smell. New research from Northwestern Medicine offers strong evidence that the brain uses predictive coding to generate “predictive templates” of specific smells — setting up a mental expectation of a scent before it hits your nostrils…”Our study confirmed the existence of predictive coding mechanisms in olfaction,” said Gottfried, senior author of the study. “We found that the entirety of the olfactory cortex we looked at did form predictive templates that were very specific to the targeted smell.”… In the study, subjects performed “odor search tasks” while being monitored inside an MRI scanner. The two scents used in the study were a watermelon smell and a Play-Doh-like smell. … Before each trial began, subjects were told which of two target smells they should try to identify. A visual countdown, informing the subjects that they should get ready to receive a specific odor was administered and then, after smelling the odor, subjects indicated by pressing a button whether they thought the target smell was present. Sometimes the target scent administered was the same as the subject was foretold, sometimes it was different, and sometimes the target scent was hidden in a mixture of other scents. … The researchers were able to look at the activity pattern of the brain before any odor arrived and found that, for trials where the target was the same, the activity pattern was more correlated than when the target was different.

When I saw this item, I immediately thought that this might have a bearing in how close might the connection between consciousness and prediction be. The picture was that our consciousness awareness is based on a prediction so that it matches in time what is happening at the time. The fraction of a second that it takes to create the conscious experience is hidden by the experience being based on a similar fraction of a second prediction.

If smell has similar prediction to vision and sound but is not usually raised to conscious awareness, then that prediction need not be an aspect of consciousness but of perception. On a closer look, the experiment only dealt with consciously registered and reported smells. It appears to still be an open question: how bound is near-future prediction to consciousness?

For a look at this prediction in more detail, here is the abstract:

Neuroscientific models of sensory perception suggest that the brain utilizes predictive codes in advance of a stimulus encounter, enabling organisms to infer forthcoming sensory events. However, it is poorly understood how such mechanisms are implemented in the olfactory system. Combining high-resolution functional magnetic resonance imaging with multivariate (pattern-based) analyses, we examined the spatiotemporal evolution of odor perception in the human brain during an olfactory search task. Ensemble activity patterns in anterior piriform cortex (APC) and orbitofrontal cortex (OFC) reflected the attended odor target both before and after stimulus onset. In contrast, prestimulus ensemble representations of the odor target in posterior piriform cortex (PPC) gave way to poststimulus representations of the odor itself. Critically, the robustness of target-related patterns in PPC predicted subsequent behavioral performance. Our findings directly show that the brain generates predictive templates or “search images” in PPC, with physical correspondence to odor-specific pattern representations, to augment olfactory perception.

Neuro-feedback

A recent paper by Zotev and group (citation below) has added another neurofeedback result to the several already on record. The subjects were instructed to contemplate happy memories and attempt to increased the BOLD signal from their left amygdala while real time feedback of the BOLD activity was relayed to them. Effective controls (sham feedback most importantly) were used.

 

What does this tell us about consciousness?

 

First, this type of learning uses consciousness – the feedback is explicit and so are the efforts to obtain the desired neural effects. Bio-feedback, in general, is a way of involving consciousness in controlling systems that are usually controlled unconsciously.

 

Secondly, the success in using the neurofeedback seems to depend somewhat in the subjects ability to bring their emotions to conscious awareness.

Across the individual subjects from the experimental group, the training effect in the left amygdala BOLD activity correlated inversely with scores on the Difficulty Identifying Feelings subscale of the Toronto Alexithymia Scale, suggesting that the better subjects rated their ability to identify their emotions, the more effectively they learned to regulate left amygdala activity via training.

 

Thirdly, The effect was different for the left and right amygdala. The left increased in BOLD activity while the right was only slightly raised.

Although the right amygdala showed a nominal increase in BOLD activity across the neurofeedback trials, this effect was only marginally significant. The statistically significant self-regulation was only specific to the left amygdala.

The functional difference between the left and right amygdala is probably due to their temporal dynamics.

Recent evidence from quantitative meta-analyses of functional neuroimaging studies has suggested a functional dissociation between left and right amygdala in terms of temporal dynamics, with the left amygdala involved in more detailed and elaborate stimulus evaluation and the right amygdala involved in rapid, short and relatively automatic detection of emotional stimuli… Consistent with this hypothesis, predominantly left-sided amygdala activation has been hypothesized to relate to left-lateralized higher cognitive processes associated with recognition and analytic processing and to cognitive representation of emotion.

 

ResearchBlogging.org

Zotev, V., Krueger, F., Phillips, R., Alvarez, R., Simmons, W., Bellgowan, P., Drevets, W., & Bodurka, J. (2011). Self-Regulation of Amygdala Activation Using Real-Time fMRI Neurofeedback PLoS ONE, 6 (9) DOI: 10.1371/journal.pone.0024522

A glimpse into the future

There is news of a development that may change the world, for the better I hope but I also fear its disuse. Chao Zhong and others have made a device that can communicate between conventional electronic devices and biological systems. In place of silicon, it uses a modified form of the polymer that is used in the exoskeletons of insects other invertebrates, hydrated maleic-chitosan. Rather than a flow of electrons, it uses a flow of protons (hydrogen ions). It therefore fits with the nature of biological electrical signals. Such a device could give birth to a whole new branch of medicine.

Here is the abstract:

Chao Zhong, et al., A polysaccharide bioprotonic field-effect transistor, Nature Communications, 2011

In nature, electrical signalling occurs with ions and protons, rather than electrons. Artificial devices that can control and monitor ionic and protonic currents are thus an ideal means for interfacing with biological systems. Here we report the first demonstration of a biopolymer protonic field-effect transistor with proton-transparent PdHx contacts. In maleic-chitosan nanofibres, the flow of protonic current is turned on or off by an electrostatic potential applied to a gate electrode. The protons move along the hydrated maleic–chitosan hydrogen-bond network with a mobility of ~4.9×10−3 cm2 V−1 s−1. This study introduces a new class of biocompatible solid-state devices, which can control and monitor the flow of protonic current. This represents a step towards bionanoprotonics.