|
|
— |
ai_timelines:neuron_firing_rates_in_humans [2022/09/21 07:37] (current) |
| ====== Neuron firing rates in humans ====== |
| |
| // Published 14 April, 2015; last updated 10 December, 2020 // |
| |
| <HTML> |
| <p>Our best guess is that an average neuron in the human brain transmits a spike about 0.1-2 times per second.</p> |
| </HTML> |
| |
| |
| |
| ===== Support ===== |
| |
| |
| ==== Bias from neurons with sparse activity ==== |
| |
| |
| <HTML> |
| <p>When researchers measure neural activity, they can fail to see neurons which rarely fire during the experiment (those with ‘sparse’ activity).<span class="easy-footnote-margin-adjust" id="easy-footnote-1-142"></span><span class="easy-footnote"><a href="#easy-footnote-bottom-1-142" title='Table 1 of<a href="http://molbio.princeton.edu/labs/images/wang/documents/shoham_segev2006_jcompphysiolA.pdf"> Shoham et al.</a> reports on a variety of investigations of sparsity in neural behavior, most of which suggest that more than 90% of neurons are sufficiently silent that they are not easily detectable. Summarizing their own results, they say &#8220;Table 1 suggests that such proportions may vary widely among different brain regions and preparations, a notion which is consistent with hierarchical, increasingly sparse neural coding schemes. Conservative estimates may, however, be possible by considering those parameters of the neuron–electrode interface that affect the detection of unit signals…suggesting a silent fraction of at least 90%.&#8221; (p. 782).Experimenters recording from a rat cortex <a href="http://www.pnas.org/content/102/39/14063.full">find</a> &#8220;Both electrical and optical recordings consistently revealed that individual neurons as well as populations of neurons display sparse spontaneous activity. Single neurons displayed low AP rates of &lt;0.1 Hz, in agreement with previous <em>in vivo</em> studies.&#8221;<a href="http://www.pnas.org/content/102/39/14063.full"> (Kerr et al 2005)</a>'><sup>1</sup></a></span> Preferentially recording more active neurons means overestimating average rates of firing. The size of the bias seems to be around a factor of ten: it appears that around 90% of neurons are ‘silent’, so unlikely to be detected in these kinds of experiments. This suggests that many estimates should be scaled down by around a factor of around ten.</p> |
| </HTML> |
| |
| |
| ==== Assorted estimates ==== |
| |
| |
| === Informal estimates === |
| |
| |
| <HTML> |
| <p>Informal websites and articles commonly report neurons as firing between <1 and 200 times per second.<span class="easy-footnote-margin-adjust" id="easy-footnote-2-142"></span><span class="easy-footnote"><a href="#easy-footnote-bottom-2-142" title='&#8216;But generally, the range for a “typical” neuron is probably from &lt;1 Hz (1 spike per second) to ~200 Hz (200 spikes per second).&#8217; -&#8216;<a href="http://neuroblog.stanford.edu/?p=4541">Astra Bryant, Ask a neuroscientist!</a> &#8211; what is the synaptic firing rate of the human brain?&#8217;</p> <p>&#8220;A typical neuron fires 5 &#8211; 50 times every second.&#8221; &#8211; <a href="http://www.human-memory.net/brain_neurons.html"><em>www.human-memory.net</em></a></p> <p>&#8220;The brain can&#8217;t handle neurons firing all the time. Neurons fire around 10x per second and already the brain is consuming 20% of the body&#8217;s energy at 2% of the body&#8217;s weight.&#8221; &#8211; <a href="http://www.quora.com/Why-dont-neurons-in-the-brain-fire-all-the-time/answer/Paul-King-2">Paul King</a>, computational neuroscientist, on Quora&#8221;Modern computer chips handle data at the mind-blowing rate of some 10^13 bits per second. Neurons, by comparison, fire at a rate of around 100 times per second or so. And yet the brain outperforms the best computers in numerous tasks.&#8221; &#8211; <a href="http://www.technologyreview.com/view/425948/massively-parallel-computer-built-from-single-layer-of-molecules/">MIT Technology Review</a>'><sup>2</sup></a></span> These sources lack references and are not very consistent, so we do not put much stock in them.</p> |
| </HTML> |
| |
| |
| === Estimates of rate of firing in human neocortex === |
| |
| |
| <HTML> |
| <p>Based on the energy budget of the brain, it <a href="/doku.php?id=ai_timelines:metabolic_estimates_of_rate_of_cortical_firing">appears</a> that the average cortical neuron fires around 0.16 times per second. It seems unlikely that the average cortical neuron spikes much more than once per second.</p> |
| </HTML> |
| |
| |
| <HTML> |
| <p>The neocortex is a large part of the brain. It accounts for around 80% of the brain’s volume<span class="easy-footnote-margin-adjust" id="easy-footnote-3-142"></span><span class="easy-footnote"><a href="#easy-footnote-bottom-3-142" title='Dunbar references<a href="http://www.ncbi.nlm.nih.gov/pubmed/7014398"> anatomical measurements from 1981</a> and<a href="http://www.cogsci.ucsd.edu/~johnson/COGS184/3Dunbar93.pdf"> writes</a> &#8220;With a neocortical volume of 1006.5 cc and a total brain volume of 1251.8 cc (Stephan et al. 1981), the neocortex ratio for humans is CR = 4.1.&#8221; (p. 682).'><sup>3</sup></a></span>, and uses 44% of its energy<span class="easy-footnote-margin-adjust" id="easy-footnote-4-142"></span><span class="easy-footnote"><a href="#easy-footnote-bottom-4-142" title='&#8220;Using the best estimate, in the normal awake state, cortex accounts for 44% of whole brain energy consumption in 200 ms, the brain’s normal energy consumption supports a strong (solid horizontal line, intercept on ordinate).&#8221; &#8211;<a href="http://www.bcs.rochester.edu/people/plennie/pdfs/Lennie03a.pdf"> Lennie 2003</a>'><sup>4</sup></a></span>. It appears to hold at least a third of the brain’s synapses if not many more<span class="easy-footnote-margin-adjust" id="easy-footnote-5-142"></span><span class="easy-footnote"><a href="#easy-footnote-bottom-5-142" title=' <p>&#8220;The average total number of synapses in the neocortex of five young male brains was 164 x 10(12) (CV = 0.17).&#8221; <a href="http://www.ncbi.nlm.nih.gov/pubmed/11418939">Tang et al, 2001</a></p> <p>&#8220;Number of synapses in cortex = 0.15 quadrillion (Pakkenberg et al., 1997; 2003)&#8221; &#8211;<a href="https://faculty.washington.edu/chudler/facts.html"> Eric Chudler</a></p> <p>&#8220;The<a href="http://en.wikipedia.org/wiki/Human_brain"> human brain</a> has a huge number of synapses. Each of the 10^<sup>11</sup> (one hundred billion) neurons has on average 7,000 synaptic connections to other neurons. It has been estimated that the brain of a three-year-old child has about 10^<sup>15</sup> synapses (1 quadrillion). This number declines with age, stabilizing by adulthood. Estimates vary for an adult, ranging from 10^<sup>14</sup> to 5 x 10^<sup>14</sup> synapses (100 to 500 trillion).&#8221; <a href="http://en.wikipedia.org/wiki/Neuron#Connectivity">Wikipedia</a> accessed April 13 &#8217;15, citing<a href="http://www.neurology.org/content/64/12/2004.extract"> Drachman, D</a> (2005). &#8220;Do we have brain to spare?&#8221;. <em>Neurology</em> <strong> |