27 December 2009

The Brain Treats Time as a Flexible Concept


"The human brain does not work on the principle of the assembly line. In processing information, it is possible that time is treated much more flexibly than previously thought," explained Wolfgang Maass, head of the Institute for Theoretical Computer Science at Graz University of Technology. _SD


Research from Max Planck Institute and Graz University of Technology suggests that the brain may store sensory input in the form of an "interference wave" for up to a second. This allows the "integration" of multiple sensory inputs before the higher brain centers get a glimpse of what is happening. The findings suggest a type of "ultra-short term memory" that functions as a type of "pre-processing" of sensory input.
Researchers usually assume that neuronal responses carry primarily information about the stimulus that evoked these responses. We show here that, when multiple images are shown in a fast sequence, the response to an image contains as much information about the preceding image as about the current one. Importantly, this memory capacity extends only to the most recent stimulus in the sequence. The effect can be explained only partly by adaptation of neuronal responses. These discoveries were made with the help of novel methods for analyzing high-dimensional data obtained by recording the responses of many neurons (e.g., 100) in parallel. The methods enabled us to study the information contents of neural activity as accessible to neurons in the cortex, i.e., by collecting information only over short time intervals. This one-back memory has properties similar to the iconic storage of visual information—which is a detailed image of the visual scene that stays for a short while (<1 s) when we close our eyes. Thus, one-back memory may be the neural foundation of iconic memory. Our results are consistent with recent detailed computer simulations of local cortical networks of neurons (“generic cortical microcircuits”), which suggested that integration of information over time is a fundamental computational operation of these networks. _PLoS
The authors refer to this phenomenon as a "liquid mind" -- alluding to the interference ripples that result from a stone being thrown into a still pond. The concept goes all the way back to Karl Pribram's "holographic memory" ideas of a few decades ago.

The research is described here, and is worth reading for a glimpse at some of the sophisticated methods being used to decipher the neural code, and to reproduce and examine neural phenomenon using machines and algorithms.

Update 28 Dec 09: Here is a report on earlier research that seems to have discovered a similar phenomenon in the human visual cortex using a sophisticated analysis of fMRI data.  The Vanderbilt researchers involved in the study refer to the phenomen as a type of "echo."   They speculate that such an ultra-short "persistence of state" phenomenon may be common throughout the cortex -- not just in the visual cortex.

Which brings us back to the concept of time, and how the human brain deals with it.  Have you ever wondered how your mind is able to maintain a moment-to-moment coherence, maintaining a train of thought or chain of logic over time?  Have you ever wondered at the persistence of certain moods and states of mind, both welcome and unwelcome?

Here is a question:  why is it when you touch your nose and your toe "simultaneously" that the touch feels simultaneous even though it takes much longer for the sensory input to reach the parietal lobe from the toe than from the nose?   The mind is capable of very creative editing of time.  A lot of pre-conscious decisions are made about how sensory (and other) phenomena will be displayed to your consciousness.

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Wednesday, 30 December, 2009  

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