Possible Reason for the High Metabolic Rate in Neurons of a Brain

Editorial

It has been found that the brain of an adult consumes about 20% of the total daily energy consumption of his whole body, although the brain cells weighs only a few presents of the body. In some highly intensive brain activities, such as in chess or go games, math competition, SAT examinations, it is estimated that the brain may consume more than 50% of the total energy consumption. What is the reason? And how does it work that the average metabolic rate of brain cells may be 5-10 times higher than that of other cells of the body?

We believe that the answer lies in the working function of brain cells, in particular, the neurons. Neuron cells in a brain works in the similar way to that of the neurons in the peripheral neural systems, e.g., the spine. For a certain moment, a neuron cell is either in an excitation state, or in a resting state. We may assume that a neuron in resting state has the same metabolic rate as those of other body cells. While in its excitation state, a neuron cell consumes more energy than in its resting state. Experiments showed that a single excitation of a neurosome, the main cell body, only lasts for 1-2 ms. Yet when playing a chess game or giving a speech, one needs seconds, minutes and even hours to analyze the dynamically acquired new information, perform comparisons with existing memory, and make decisions. These brain activities require that short memories have to maintains right information data for seconds to hours. One sees here a huge mismatch in time scale: Between a few milliseconds and minutes or hours, a gap of 3-7 orders of magnitude. The nature should have found a way to solve the mismatch in time. Then, what is the feasible working mechanism?

We have presented a hypothesis, that the information restored in a brain are memorized in the forms of “two-dimensional (2D) patterns” of neurosomes, where each two neighboring neurosomes are strongly connected with their synapses [1]. According to this model, after receiving information from various body sensors, in the Sensory Layer (S) of the cortex certain groups of neurosomes are excited, forming a 2D pattern, as schematically illustrated in (Figure 1a). This 2D pattern in the sensory layer then projects into a Memory Layer (M1) through the vertical dendrites, as shown in (Figure 1b). The pattern is copied based on the fact that the synaptic connection between two neurosomes is strengthened when it receives electrical signals from the two neurons simultaneously. The sensory layer is cleared for receiving next sensing data. Then the 2D pattern copied in M1 is further projected to a second Memory Layer (M2), as shown in (Figure 1c). To maintain the data stored in the 2D pattern, the pattern should be echoed back to M1, and the processes of 1b and 1c need to repeat again and again. This echoing and oscillating mechanism between memory layers (M1→M2→M1→M2→……) ensures a temporary memory at the seconds and minutes level, in spite of the short transient excitation duration for each layer of neurons (i.e., a few ms).

    

    

    Figure 1: Schematic illustration of the forming and echoing processes for
temporary memory. a) A 2D pattern of excited neurosomes (highlighted with
grey stars) is formed on the Sensory Layer (S), corresponding to the data
obtained from body sensors. This neurosome pattern projected into the first
Memory Layer (M1) through dendrites, causing simultaneous excitation of
neurons in this layer (orange stars) with a pattern similar to that on S layer.
b) The 2D pattern is further projected to the second Memory Layer (M2)
through dendrites. c) To maintain the information, the 2D pattern of excited
neurosomes is echoed back to M1 layer. Repeating b) and c) keeps the data
stored in the 2D pattern as temporary memory.