Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
Thinking About Time
Conscious beings have a built-in feeling of time. Time feels continuous and feels ordered in a chronology of events.
Neither the continuity of time (all the astronomical, geological and biological "clocks" are quantized in nature) nor the ordering of time can be easily explained. They are both quite "unnatural".
Nature uses different clocks at different levels of organization. There are seasons (that trigger life stages such as hibernation or pollination). There is the alternation of day and night (sleep, feeding). Then there are countless body clocks that regulate everything from heartbeat to eyesight. At the lowest level of organization there are clocks for the cells. Since the feeling of time is in the brain, the neurons are particularly interesting kinds of cells. The hippocampus is a region of the brain that is crucial for the maintenance of long-term memories, and therefore to the sense of flowing time.
The "clock" of the hippocampus is represented by theta oscillations. The Greek neurologist Thanos Siapas ("Hippocampal theta oscillations are traveling waves", 2009) has shown that they are not synchronized throughout the hippocampus. Taken together, the theta oscillations constitute a traveling wave through the hippocampus. They travel at a speed of about 100 mm/sec, which means that their spatial length-wave is approximately the size of the hippocampus. In other words, they behave like the rhythm of day and night around the various time zones of the Earth. This wave of theta oscillations "paces" the hippocampus in a manner similar to a regular progression of time zones.
Biological organisms need to deal with time at at least twelve orders of magnitude, from 10 to the -6th seconds (neurons) to 10 to the 6th seconds (days). Humans use the same technological artifact (clocks) to measure time at all of these levels. The brain, however, does not seem to have a clock. There is no central timekeeper in the brain. The brain uses different mechanisms to measure time depending on time scale. There are several techniques that the brain can use to measure time. The first one is the same one used by clocks: an oscillator and a counter. The second one is to encode timing in the firing rate of neurons. A third one, propounded by the US neurologist Dean Buonomano ("State-dependent Computations"), is that our perception of time might be a consequence of the organization of neurons in networks. Timing emerges in neural networks as a result of their dynamics in the face of stimuli. The strengths of synapses change in time like ripples in a pond. Just like the extent of a ripple is an indication of how much time has elapsed since the pebble hit the water, so the dynamics of synapses can be used to "measure" elapsed time. Unlike clocks that "tick" in a linear manner, the brain does not have a ticking clock and therefore does not keep track of time in a linear manner.
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