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Archive for October 2009

Sense of time

ScienceDaily has an item on research by A. Graybiel, ‘Neural representation of time in corticobasal ganglia circuits’. ( here )

Keeping track of time is one of the brain’s most important tasks. As the brain processes the flood of sights and sounds it encounters, it must also remember when each event occurred. But how does that happen? … For decades, neuroscientists have theorized that the brain “time stamps” events as they happen, allowing us to keep track of where we are in time and when past events occurred. However, they couldn’t find any evidence that such time stamps really existed — until now … The research team trained two macaque monkeys to perform a simple eye-movement task. After receiving the “go” signal, the monkeys were free to perform the task at their own speed. The researchers found neurons that consistently fired at specific times — 100 milliseconds, 110 milliseconds, 150 milliseconds and so on — after the “go” signal … The neurons are located in the prefrontal cortex and the striatum, both of which play important roles in learning, movement and thought control. … We have sensory receptors for light, sound, touch, hot and cold, and smell, but we don’t have sensory receptors for time. This is a sense constructed by the brain.”

It strikes me that this clock system would be one more or less dedicated to motor processes because: it measures very short durations; it is found in the prefrontal cortex/striatum system; and it is more accurate than flexible. The conscious feeling of the passage of time may be from another system derived from this one or even a completely separate system.

The New Scientist had an article on time perception (here) by D. Fox that reviews a number of experiments.

  • R. VanRullen showed that vision is framed rather than continuous and the frame rate is about 13 per second. He found that the visual area of the right inferior parietal lobe generated a 13 Hertz wave. The question then was - is the framing global or independent for each preceived object? Visual illusions showed that framing is not global.

This implies that there is not a single “film roll” in the brain, but many separate streams, each recording a separate piece of information. What’s more, this way of dealing with incoming information may not apply solely to motion perception. Other brain processes, such as object or sound recognition, might also be processed as discrete packets.”

  • Using very weak stimuli he showed that there are windows of perception.

… found that the likelihood of them noticing the light depended on the phase of another wave in the front of the brain, which rises and falls about 7 times per second. It turned out that subjects were more likely to detect the flash when the wave was near its trough, and miss it when the wave was near its peak. There’s a succession of ‘on’ periods and ‘off’ periods of perception. Attention is collecting information through snapshots … So it seems that each separate neural process that governs our perception might be recorded in its own stream of discrete frames. But how might all these streams fit together to give us a consistent picture of the world?”

  • E. Poppel looked at this problem, proposed blocks of frames and found some experimental evidence for the blocks.

… separate snapshots from the senses may feed into blocks of information in a higher processing stream. He calls these the “building blocks of consciousness” and reckons they underlie our perception of time. … It’s an appealing idea, since patching together a chronological order of events hitting our senses is no mean feat. Sounds tend to be processed faster than images, so without some sort of grouping system we might, say, hear a vase smashing before we see it happen. Pöppel’s building blocks of consciousness would neatly solve this problem: if two events fall into the same building block, they are perceived as simultaneous; if they fall into consecutive buildings blocks, they seem successive. Perception cannot be continuous because the limits of neural processing. …. A space of 30 to 50 milliseconds is necessary to bring together in one time-window the distributed activity in the neural system.”

There is also interesting discussion of whether our sense of time becoming slower or faster is a function of brain speed or of memory density. And finally exploration of the idea that some symptoms of schizophrenia may be due to faulty timekeeping.

The maps in our minds

ScienceDaily reports research from the Norwegian University of Science and Technology on the mapping facility of the brain. (here) The research was done on rats but the investigators believe it applies to humans because the hippocampus and entorhinal cortex (site of spatial mapping) are the oldest and best conserved areas, across evolution, of all the forebrain structures.

The rat brain mapping system thus consists of a series of small maps, not just a single large one. … A recently discovered cell type, border cells, which are active along certain walls in a given environment, may shed light on this question. Border cells describe the limits of how an environment ends and another begins.

The same report includes research by K. Kjelstrup and how the multiple maps are used.

We need maps of varying resolution, some small detailed maps, and other, larger rougher maps … and the brain sorts these very systematically.”…The maps are stored as extremely thin cards in a deck in the hippocampus, the area that is regarded as the brain’s memory focal point. The deck is sorted by rank, so that the fine-grained detail maps located at the top, with the biggest, most coarsely drawn maps the further down in the deck that you come.

So it appears that in its simplest (probably too simple) visualization the mapping facility with its four types of cell (place, grid, direction, border) works in the following way:

- We recognize which map we are in from the sensory match with a place using place cells and that activates a memory map in the hippocampus

- This current map is laid out on the grid cell array in the entorhinal cortex. The grid and place cells indicating where we are on the map and the direction cells indicating our heading (in orientation or movement). Reaching border cells indicates the need for a new map.

- A new map is fetched from the hippocampus as indicated by the heading and/or the place information.

- New maps would be formed (as memories) and old ones updated as needed.

What aspects of all this would enter consciousness? We are aware of where we are usually and of our heading. When we do not, we have the fringe feeling of being lost or a fringe feeling of being in an entirely new place, or both. But although usually we have this sense of where we are, it is usually not the focus of attention – in awareness but not in focus.

Fruits of introspection

T. Natsoulas has kindly sent me an email with a paper attached, ‘On the Intrinsic Nature of States of Consciousness: attempted Inroads from the First-Person Perspective’, T Natsoulas, The Journal of Mind and Behavior, 2001. The paper deals with the ideas of W. James from the 1890s and F. Bradley from the 1910s, both having explored consciousness using introspection as their tool.

I have not had much hope that introspection would yield much except the preconceptions of the introspector. Maybe I was wrong, and a diligent, intelligent, open-minded person can learn something about the nature of consciousness by introspection. James seems to have found in his introspection reason to believe four very important ideas: consciousness is about awareness, it is a stream of individual moments/states/pulses of mentality, there is only one stream at a time that we can experience, and finally, a individual state in the stream has an indivisible unity. Well I think that is surprisingly good returns for just thinking about one’s own thinking, with practically no additional material from psychology or neurology.

Looking forward to a generally acceptable theory of consciousness – the theory must be able to describe consciousness in ways and vocabularies that fit with:

  • some theory of the brain function and its biology, chemistry and physics,

  • some theory of mental cognition, emotion and memory in psychological terms,

  • a way to philosophically interpret our own introspective experiences.

Near death EEG spikes

MindHacks (here) posted information on a study published by L.S. Chawla and others, ‘Surges of Electroencephalogram Activity at the Time of Death: A Case Series’. Here is the brief report:

Level of consciousness at the end of life in critically ill patients is poorly characterized. We report a case series of seven patients who were neurologically intact before the decision to withdraw care due to extensive systemic critical illness. As part of our end-of-life care protocol, bispectral index (BIS) monitor (Aspect Medical Systems, Newton, MA) or SEDline™ (Hospira, Lake Forest, IL) monitoring devices are placed on each patient to ensure adequate comfort. Both monitoring systems use an integer-based system (BIS or PSI, respectively) to reflect the level of consciousness/effect of anesthesia. In each case, loss of blood pressure, as monitored by indwelling arterial line, was followed by a decline in BIS/PSI activity followed by a transient spike in BIS/PSI activity that approached levels normally associated with consciousness. This spike in electroencephalogram (EEG) activity had short duration and the activity then declined to a level of activity associated with burst suppression. In one case of a patient who had a SEDLine™ device, we were able to capture and analyze the raw EEG signal, and confirm that the EEG waveform was not artifact, and in fact a high frequency waveform was present during the spike activity. We speculate that this level of BIS/SEDline™ activity is related to the cellullar loss of membrane polarization due to hypoxemia. We further speculate that since this increase in electrical activity occurred when there was no discernable blood pressure, patients who suffer “near death” experiences may be recalling the aggregate memory of the synaptic activity associated with this terminal but potentially reversible hypoxemia.

More data would be needed to confirm this explanation of near-death experiences. One can understand how, if the whole brain is active, that the effect might seem to resemble a very bright light or your ‘whole life passing before your eyes’.

Some clarity on rewards

I have been confused by the way or ways the brain has to make value judgments. Mindblog (here) has pointed to the abstract of a paper by de Brujin and others:

For social beings like humans, detecting one’s own and others’ errors is essential for efficient goal-directed behavior. Although one’s own errors are always negative events, errors from other persons may be negative or positive depending on the social context. We used neuroimaging to disentangle brain activations related to error and reward processing, by manipulating the social context (cooperation or competition). Activation in posterior medial frontal cortex (pMFC) was increased for all errors, independent of who made the error or the reward outcome. Conversely, activity in striatum was modulated by reward, independent of whether the action was erroneous or not. The results demonstrate a clear distinction between error and reward processing in the human brain. Importantly, the current study indicates that error detection in pMFC is independent of reward and generalizes beyond our own actions, highlighting its role in optimizing performance in both individual and joint action.

That is a lot less confusing.

Effects of brain waves

Eurekalert reports on research by A. Pogosyan and others (here) that gives evidence that brain waves can cause effects in brain cells.

“At last we have some direct experimental proof that brain waves influence behavior in humans, in this case how fast a movement is performed. The implication is that it is not just how active brain cells are that is important, but also how they couple their activity into patterns like beta activity… The electrical current used increased normal beta activity, a wave that earlier studies linked to sustained muscle activities, such as holding a book. Beta activity drops before people make a move.

Unlike most previous work, which used constant brain stimulation, the new study employed an oscillating current, more like that underlying normal brain activity. As a result, people’s fastest times on the computer task were 10 percent slower… researchers were surprised that the electrical currents used in the study—which were very small and imperceptible to the participants—could have such a measurable effect… The current findings provide the first interventional evidence of a causal link between increased beta synchrony and the slowing of voluntary movement in otherwise healthy individuals, the researchers report, noting that earlier studies have shown altered brain waves to influence memory. ”

This will certainly complicate how we view feedback loops in the brain. Brain waves might not just be indicators of what is be going on, but may be players in their own right.

Hard-problem mindset

E. Thompson in the philosophical blog, Brains, posted on the ‘Hard-Problem’. (here) He looks at Chalmers’ ideas on consciousness and quotes a Chalmers definition:

The really hard problem of consciousness is the problem of experience. When we think and perceive, there is a whir of information-processing, but there is also a subjective aspect. As Nagel (1974) has put it, there is something it is like to be a conscious organism. This subjective aspect is experience. When we see, for example, we experience visual sensations: the felt quality of redness, the experience of dark and light, the quality of depth in a visual field.”

Thompson pin points the weaknesses in Chalmers’ statement:

First, as suggested in the second sentence of the quote above, Chalmers assumes that experience cannot be a matter of information processing. If you read his book, he explicitly assumes (in the Introduction) that experience cannot be generated by information processing, neuronal activity, standard biology. Given that assumption, is it any surprise that he thinks experience is a really hard problem? Chalmers has the stones to claim that those not working within this loaded conception of consciousness aren’t ‘taking consciousness seriously’

Of course, the biologists who are studying consciousness are taking it seriously and believe that ’standard biology’ can generate experience. They are not playing word games.

Thompson goes on to the use of the hard-problem idea by others:

Despite these seemingly obvious problems with his approach, I observed with dismay as the phrase “What about the hard problem?” spread like syphilis over the amateur philosophy of consciousness landscape. It became a kind of cognitive creativity sink, an easy knee-jerk response to any discussion of consciousness. Psychologists and neuroscientists are now required, by law, to address the “hard problem” in the first or final chapter of their books on consciousness. It’s a bit ridiculous.

Resolving conflicting intentions

ScienceDaily reported (here) on a study by E. Morsella, The Essence of Conscious Conflict: Subjective Effects of Sustaining Incompatible Intentions.

The results demonstrated that merely preparing to perform an incompatible action, for example preparing to move simultaneously left and right, triggered stronger changes in awareness than preparing to perform a compatible action or experiencing a conflict that does not engage the muscles that move our bodies.”

Projecting our actions into the near future would be a good way to identify impossible combinations of actions. Heightened awareness of these conflicts would highlight the problems. Morsella proposes a theory which predicts that the primary role of consciousness is to bring together competing demands on skeletal muscle.

If the brain is like a set of computers that control different tasks, consciousness is the Wi-Fi network that allows different parts of the brain to talk to each other and decide which action ‘wins’ and is carried out… The study finds that we are only aware of competing actions that involve skeletal muscles that voluntarily move parts of the body, the bicep for example, rather than the muscles in the digestive tract or the iris of the eye….The results give credence to an interesting idea that ‘thinking is for doing,’ a framework psychologists are using to explore the link among consciousness, perception and action.”

Colour binding

Science Daily (here) reports on a paper by S. Shevell, Color-Binding Errors during Rivalrous Suppression of Form. The work shows how the brain integrates the multiple features of an object, such as shape, color, location and velocity, into a unified whole.

The brain’s neural mechanisms keep straight which color belongs to what object, so one doesn’t mistakenly see a blue flamingo in a pink lake. But what happens when a color loses the object to which it is linked? Research at the University of Chicago has demonstrated, for the first time, that instead of disappearing along with the lost object, the color latches onto a region of some other object in view – a finding that reveals a new basic property of sight.

The research shows that the brain processes the shape of an object and its color in two separate pathways and, though the object’s shape and color normally are linked, the neural representation of the color can survive alone. When that happens, the brain establishes a new link that binds the color to another visible shape.”

It is as if entities are stored in working memory with ‘tags’ to their attributes and these ‘tags’ can sometimes be lost, misplaced or (in synesthesia) be applied to inappropriate entities. However, there must be two sorts of ‘tag’: the vivid attributes of conscious sensory experience which presumably still have access to the primary sensory areas of the cortex, and the much less vivid attributes of memory and imagination where the primary sensory input is long gone or never was.

Dead fish and voodoo

For a little while there having been questions about the statistical processing of fMRI scans. These play along side less sensible questions. We have:

  1. It is no clear exactly what causes the changes measured with fMRI and so the results due not have meaning.

  2. The way scan results are reported in the press as ‘areas for x’ is misleading.

  3. There are problems with the significance levels for large numbers of statistical tests.

  4. There are problems with the independence of statistical tests.

The first two are red herrings. We do not have to know exactly how an effect is caused as long as we have a general idea and correlation with other effects. The scans do have meaning – changes in the amount of neural activity. What way the popular press report research has nothing to do with the validity of the work. Calling new things ‘miracle drugs’ does not have any effect on how well or badly they may treat a disease.

The statistical problems were reviewed recently by C. Chatham at Developing Intelligence (here). He reviews the Dead Fish experiment of Bennett and the Voodoo Correlation paper of Vul. Here is his conclusion:

To summarize, the dead fish study is a point about first-pass analysis, which almost every paper I’ve ever seen does correctly. The papers that don’t always note that the result failed to pass multiple comparisons or cluster correction, and typically discuss those results with caution. On the other hand, “voodoo correlations” is a point about nonindependence in statistical tests. This has not always been done correctly, and has not always been reported clearly. Moreover it primarily affects only a subset of correlations between brain and behavior - and not the vast majority of work in fMRI, which has to do with task-brain relationships.

I believe that a good protection against being taken in by reports of research that turn out to be shoddy is to be very, very slow to accept or reject any single result. What convinces me is not any particular chain of logic or single result but a fabric of results by various people, with various methods and various view points. When such a fabric builds up, then it can be accepted.