Experiments reveal only a small fraction of the actual functional activity performed by our brain.2015 The Authors. Published by the Royal Society under the terms of the Creative Commons AttributionLicense http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.In this essay, I review the evidence that persuades me of the importance of intrinsic activity and then briefly survey the material presently available regarding its properties and functions. The story is incomplete but rich with opportunities for future research that will be most productive if conducted in a climate of mutual respect for different levels of analysis.(b) Sensory informationComplementary insight on the importance of intrinsic activity comes from a consideration of sensory information. It may surprise some to learn that visual information is significantly compressed as it passes from the eye to the visual cortex [24,25]. Thus, of the information available from the environment, only about 1010 bits s21 are deposited in the retina. Because of a limited number of axons in the optic nerves (approx. 1 million axons in each) only 106 bits s21 leave the retina and only 104 make it to layer IV of V1. These data clearly leave the impression that visual cortex receives a very compressed HMPL-012 dose representation of the world, a subject of more than passing interest to those interested in the processing of visual information [26]. Parenthetically, it should be noted that estimates of the bandwidth of conscious awareness itself (i.e. what we `see’) are in the range of 100 bits s21 or less [25]. Reinforcing this impression of the brain’s `isolation’ is the fact that the number of synapses in the lateral geniculate nucleus of the thalamus and in layer IV of primary visual cortex devoted to incoming visual information is less than 10 of the total number of synapses in both locations [27]. Various proposals have been made concerning the interpretation of these anatomical data [28,29] but the fact remains that the brain must interpret, respond to and even predict environmental demands from seemingly impoverished data. An explanation for its success in doing so must lie in significant measure with intrinsic brain processes that link representations residing broadly within brain systems to incoming sensory information [30]. Vernon Mountcastle, one of the preeminent neurophysiologists of the twentieth century, summed up the situation nicely: `Each of us believes himself to live directly within the world that surrounds him, to sense its objects and events precisely, and to live in real and current time. I assert that these are perceptual illusions. Sensation is an abstraction, not a replication, of the real world’ [31].rstb.royalsocietypublishing.org2. Adjudicating the merits of intrinsic activity(a) CostOne of the most persuasive arguments for the importance of intrinsic activity emerges from a consideration of its relative cost in terms of brain get Tulathromycin A energy consumption. In the average adult human, the brain represents about 2 of the total body weight yet it accounts for 20 of all the energy consumed [3,4], 10 times that predicted by its weight alone. Relative to this very high rate of ongoing energy consumption in the resting state, the additional energy consumption associated with changes in brain activity is remarkably small, often less than 5 of the baseline level of activity [5]. From these data, it is clear that the.Experiments reveal only a small fraction of the actual functional activity performed by our brain.2015 The Authors. Published by the Royal Society under the terms of the Creative Commons AttributionLicense http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.In this essay, I review the evidence that persuades me of the importance of intrinsic activity and then briefly survey the material presently available regarding its properties and functions. The story is incomplete but rich with opportunities for future research that will be most productive if conducted in a climate of mutual respect for different levels of analysis.(b) Sensory informationComplementary insight on the importance of intrinsic activity comes from a consideration of sensory information. It may surprise some to learn that visual information is significantly compressed as it passes from the eye to the visual cortex [24,25]. Thus, of the information available from the environment, only about 1010 bits s21 are deposited in the retina. Because of a limited number of axons in the optic nerves (approx. 1 million axons in each) only 106 bits s21 leave the retina and only 104 make it to layer IV of V1. These data clearly leave the impression that visual cortex receives a very compressed representation of the world, a subject of more than passing interest to those interested in the processing of visual information [26]. Parenthetically, it should be noted that estimates of the bandwidth of conscious awareness itself (i.e. what we `see’) are in the range of 100 bits s21 or less [25]. Reinforcing this impression of the brain’s `isolation’ is the fact that the number of synapses in the lateral geniculate nucleus of the thalamus and in layer IV of primary visual cortex devoted to incoming visual information is less than 10 of the total number of synapses in both locations [27]. Various proposals have been made concerning the interpretation of these anatomical data [28,29] but the fact remains that the brain must interpret, respond to and even predict environmental demands from seemingly impoverished data. An explanation for its success in doing so must lie in significant measure with intrinsic brain processes that link representations residing broadly within brain systems to incoming sensory information [30]. Vernon Mountcastle, one of the preeminent neurophysiologists of the twentieth century, summed up the situation nicely: `Each of us believes himself to live directly within the world that surrounds him, to sense its objects and events precisely, and to live in real and current time. I assert that these are perceptual illusions. Sensation is an abstraction, not a replication, of the real world’ [31].rstb.royalsocietypublishing.org2. Adjudicating the merits of intrinsic activity(a) CostOne of the most persuasive arguments for the importance of intrinsic activity emerges from a consideration of its relative cost in terms of brain energy consumption. In the average adult human, the brain represents about 2 of the total body weight yet it accounts for 20 of all the energy consumed [3,4], 10 times that predicted by its weight alone. Relative to this very high rate of ongoing energy consumption in the resting state, the additional energy consumption associated with changes in brain activity is remarkably small, often less than 5 of the baseline level of activity [5]. From these data, it is clear that the.