One picture is worth at least a million neurons

Ifat Levy, Uri Hasson, Rafael Malach

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


How many neurons participate in the representation of a single visual image? Answering this question is critical for constraining biologically inspired models of object recognition, which vary greatly in their assumptions from few "grandmother cells" [1] to numerous neurons in widely distributed networks [2]. Functional imaging techniques, such as fMRI, provide an opportunity to explore this issue, since they allow the simultaneous detection of the entire neuronal population responding to each stimulus. Several studies [3-6] have shown that fMRI BOLD signal is approximately proportional to neuronal activity. However, since it provides an indirect measure of this activity, obtaining a realistic estimate of the number of activated neurons requires several intervening steps. Here, we used the extensive knowledge of primate V1 to yield a conservative estimate of the ratio between hemodynamic response and neuronal firing. This ratio was then used, in addition to several cautious assumptions, to assess the number of neurons responding to a single-object image in the entire visual cortex and particularly in object-related areas. Our results show that at least a million neurons in object-related cortex and about two hundred million neurons in the entire visual cortex are involved in the representation of a single-object image.

Original languageEnglish (US)
Pages (from-to)996-1001
Number of pages6
JournalCurrent Biology
Issue number11
StatePublished - Jun 8 2004
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Agricultural and Biological Sciences
  • General Biochemistry, Genetics and Molecular Biology


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