When You Read "It Is Widely Believed," Suspect a Dubious Belief Custom

We can classify several different types of scientific truth claims, along with some tips on how to recognize the different types. 

Type of truth claim	How to recognize it
Citation of established fact	Typically occurs with a discussion of the observational facts that proved the claim.
Citation of a claim that is not yet established fact	Typically occurs with phrases such as “scientists believe” or “it is generally believed” or an appeal to a “scientific consensus.” The claim of a “scientific consensus” is often unfounded, and there may be many scientists who do not accept the claim.
Citation of a claim that has little basis in observations, and that there may be good reasons for doubting	Often occurs with a phrase such as “it is widely believed,” or maybe a more confident-sounding phrase like “it is becoming increasingly clear” or “there is growing evidence.”

Claims that memories are stored in synapses fall into the third of these categories. To show that, I may cite some of the many times in which writers or scientists suggested that memories are stored in synapses, and merely used the weak phrase "it is widely believed" as their authority. 

• "It is widely believed that synaptic plasticity mediates learning and memory"  (link). 
• "It is widely believed that synapses in the forebrain undergo structural and functional changes, a phenomenon called synaptic plasticity, that underlies learning and memory processes" (link).
• "It is widely believed that synaptic modifications underlie learning and memory" (link).
• "As with other forms of synaptic plasticity, it is widely believed that it [spike-dependent synaptic plasticity] underlies learning and information storage in the brain" (link).
• "It is widely believed that memories are stored as changes in the number and strength of the connections between brain neurons, called synapses" (link).
• "It is widely believed that modifications to synaptic connections – synaptic plasticity – represent a fundamental mechanism for altering network function, giving rise to phenomena collectively referred to as learning and memory" (link).
• "It is widely believed that encoding and storing memories in the brain requires changes in the number, structure, or function of synapses"  (link).
• "It is widely believed that long-term changes in the strength of synaptic transmission underlie the formation of memories" (link).
• "It is widely believed that the brain's microcircuitry undergoes structural changes when a new behavior is learned" (link).
• "It is widely believed that long-lasting changes in synaptic function provide the cellular basis for learning and memory in both vertebrates and invertebrates (link).
• "It is widely believed that the brain stores memories as distributed changes in the strength of connections ('synaptic transmission') between neurons" (link).
• "It is widely believed that the long-lasting, activity-dependent changes in synaptic strength, including long-term potentiation and long-term depression, could be the molecular and cellular basis of experience-dependent plasticities, such as learning and memory" (link).
• "It is widely believed that a long-lasting change in synaptic function is the cellular basis of learning and memory" (link).
• "It is widely believed that the modification of these synaptic connections is what constitutes the physiological basis of learning" (link).
• "It is widely believed that memory traces can be stored through synaptic conductance modification" (link).
• "It is widely believed that memories are stored in the synaptic strengths and patterns between neurons" (link).
• "It is widely believed that long-term changes in the strength of synaptic connections underlie learning and memory" (link).
• "It is widely believed that long-term synaptic plasticity plays a critical role in the learning, memory and development of the nervous system" (link).
• "It is widely believed that learning is due, at least in part, to long-lasting modifications of the strengths of synapses in the brain" (link).
• "It is widely believed that long-term memories are stored as changes in the strengths of synaptic connections in the brain" (link). 
• "It is widely believed that activity-dependent modification of synapses is the brain's primary mechanism for learning and memory" (link).
• "It is widely believed that synaptic modifications are one of the factors underlying learning and memory" (link).
• "Learning, it is widely believed, is based on changes in the connections between nerve cells" (link).
• "It is widely believed that memories are stored as changes in the number and strength of the connections between brain cells (neurons)" (link).
• "It is widely believed that memories are stored as changes in the strength of synaptic connections between neurons" (link). 
• "It is widely believed that memory formation is based on changes in synapses" (link).

There is no good evidence that any memories are stored in synapses or stored through a strengthening of synapses or stored by a modification of synapse weights, or stored anywhere in the human brain through any means. No one has any understanding or any credible coherent theory of how learned information or episodic memories could ever be stored using synapses or any other part of the brain. We know of the strongest reason for rejecting all of the claims in the bullet list above, which is that the average lifetime of the proteins in synapses is only about two weeks or less.  The proteins in synapses last an average of only about a thousandth of the longest length of time that humans can remember things (50 years or more). Moreover, humans can form permanent new memores instantly, which could never occur if forming such memories required synapse strengthening (something that would take minutes or hours, because it would require the synthesis of new proteins). 

The examples in the bullet list above are simply an example of a speech custom. Scientists and science writers have got in the bad habit of saying something like "it is widely believed that memory formation occurs through changes in synapses." The fact that such a large fraction of the writers repeating this myth use the same language phrasing (including the phrase "it is widely believed") shows that what is going on is mainly people parroting what other people have said, rather than independently reaching intelligent judgments based on facts.  I may note that in not a single one of these cases has any of these writers even claimed a scientific agreement, or even a majority of scientist opinion.  Claiming that something is "widely believed" is to make a claim much weaker than claiming "almost everyone believes" or "most people believe." When people haven't got much of a case, they use phrases like "it is widely believed." 

In general, when you hear or read someone using the phrase "it is widely believed," you should suspect a dubious belief custom or a misguided belief.  For example, if someone says "it is widely believed you can't trust men from that country," he is saying something that means very little. And if someone says, "it is widely believed that the thirteenth day of the month is unlikely," you are probably just hearing an old wives tale.  Because they all use the weak shaky phrase "it is widely believed," every statement in my bullet list above should be treated as a "red flag" indicating a lack of good evidence.