Judging from its index, Dowling's 295-page book makes no mention of the topics of thinking, abstract thinking, ideas, concepts, recall, recognition or reasoning (none of which have an index entry). The topic of thinking and consciousness doesn't really appear until the last chapter in the book, which starts out on page 253 with this very silly statement: "Human consciousness is just about the last surviving mystery." The worlds of cosmology, physics, psychology, history and biology are actually filled with 1001 great mysteries that humans don't understand.
Our biologists do not even know how the simplest prokaryotic cell could have originated, and they do not have a credible account of how eukaryotic cells originated (only a very unbelievable tall tale). Our biologists do not even know what causes a cell to split into two copies of itself; they do not know what causes polypeptide chains to fold into the three-dimensional shapes of proteins; and they do not know what causes a fertilized ovum to progress to become a human baby. Our biologists do not know how humans are able to remember things for 50 years (despite rapid protein turnover in synapses), and how humans can instantly remember things they learned or experienced decades ago. Our biologists do not have credible explanations of the origin of humans, the origin of language, or the origin of complex biological innovations (they merely have achievement legends about some of these things). So it is most ridiculous when biologists such as Dowling say things such as "Human consciousness is just about the last surviving mystery," thereby making the modern scientist sound as if he knows a thousand times more than he actually does.
Equally ridiculous is Dowling's assertion on page 253 that the following mysteries "have been tamed": "the mystery of the origin of the universe, the mystery of life and reproduction, the mystery of the design to be found in nature, the mysteries of time, space and gravity." No, these mysteries have not at all been "tamed." I will have a future post on why biologists do not actually understand 90% of sex and reproduction; and I may note that gravity is so little understood that it does not even have a place in the standard model of physics.
Dowling asserts on page 260, "Clearly our rich mental life depends on higher cortical function," but he presents no good evidence to back up this claim. We actually know that crows are quite smart, despite having very small brains that lack a neocortex. We know also that damage to the prefrontal cortex has little effect on mental abilities, as I documented quite thoroughly in this post, which includes references to many neuroscience papers.
The assertion quoted above is followed by an appeal to experiments of the scientist Wilder Penfield in which people recalled things after having parts of their brains electrically stimulated. Dowling states on page 262:
Stimulating particular parts of the cortex evoked visual and auditory sensations along with emotions and feelings. Clearly these experiences were evoked from within.
But it's actually not known whether visual images arising from such stimulation are memories, hallucinations, or simply vivid imagination. A review of 80 years of experiments on electrical stimulation of the brain uses the word “reminiscences” for accounts that may or may not be memory retrievals. The review tells us, “This remains a rare phenomenon with from 0.3% to 0.59% EBS [electrical brain stimulation] inducing reminiscences.” The review states the following:
We observed a surprisingly large variety of reminiscences covering all aspects of declarative memory. However, most were poorly detailed and only a few were episodic. This result does not support theories of a highly stable and detailed memory, as initially postulated, and still widely believed as true by the general public....Overall, only one patient reported what appeared to be a clearly detailed episodic memory for which he spontaneously specified that he had never thought about it....Overall, these results do not support Penfield's idea of a highly stable memory that can be replayed randomly by EBS. Hence, results of EBS should not, at this stage, be taken as evidence for long-term episodic memories that can sometimes be retrieved.
What is quite possible is that the brain is like some reducing valve or faucet, and that the brain reduces your memory and imagination, just as a faucet can limit a flow of water to a mere trickle. Such a reduction may make you more likely to focus on the crummy little details of daily living. In such a case, electrically stimulating some part of the brain might limit that reduction effect or suppression effect, increasing recall and imagination that are not at all caused by the brain. Similarly, hitting a faucet with a hammer may increase its flow of water, but the water isn't coming from inside the little faucet.
Dowling then attempts to insinuate on page 262 that brain studies tell us that "certain neurons in the prefrontal cortex become active during the time when the monkey is remembering" where a target is. But, to the contrary, this post (which includes links to many scientific studies) summarizes the evidence that brains show no real signs of looking different or working harder when humans are thinking or recalling things. Since almost all neurons in the brain are continually active, we should never draw a conclusion based on the mere activity of some neurons while a brain was remembering.
Dowling then confesses on page 263 that "we are just at the beginning of understanding how neural activity...might relate to consciousness." On the next page he states, "The neural basis of human consciousness seems beyond our experimental reach for the time being." A few pages later the book ends. It has not provided anything remotely like an explanation for how cells could yield cognition. Dowling hasn't even taken a stab at explaining such a thing. He has a chapter entitled "From Brain to Mind," but it deals with visual perception. Of course, there's so much more to "the mind" than just visual perception: imagination, intelligence, abstract thinking, recall, self-hood, and so forth.
On the topic of memory, Dowling tries to drop little bits of information here and there supporting the idea that the brain is a storage place for our memories. Like almost all neuroscientists writing books on the brain, he mentions the case of patient H.M., who had trouble forming memories after suffering damage to part of his brain called the hippocampus (although he could recall memories learned before that damage). The reliance of neuroscientists on this one case is not at all scientific. You may establish a cause and effect hypothesis if you correlate many examples of a cause and effect (such as correlating many examples of people smoking with many examples of people having lung cancer). But it is rather ridiculous to speak (as neuroscientists often do) as if we know some memory problem in someone was caused by some problem in part of his brain. You would need many examples of such a thing before having confidence that the two were causally related. Similarly, it would be absurd to suggest that our memories are stored in the root canals of our teeth because of the historical case of one patient who had a serious memory problem after having a root canal procedure.
As usual, the story of HM is wrongly told. Dowling tells us that patient HM "no longer could remember events or facts for more than a few minutes." But a 14-year follow-up study of patient HM (whose memory problems started in 1953) actually tells us that HM was able to form some new memories. The study says this on page 217:
In February 1968, when shown the head on a Kennedy half-dollar, he said, correctly, that the person portrayed on the coin was President Kennedy. When asked him whether President Kennedy was dead or alive, and he answered, without hesitation, that Kennedy had been assassinated...In a similar way, he recalled various other public events, such as the death of Pope John (soon after the event), and recognized the name of one of the astronauts, but his performance in these respects was quite variable.
Our neuroscientists keep misinforming us about patient HM because it serves their dogmatic purposes to do so. Even if you were to prove that destruction of the hippocampus prevents the formation of new memories, that would not at all prove that memories are stored in the brain. The hippocampus could simply be kind of a springboard that helps propel sensory experience into some unknown memory storage reality outside of the brain.
On page 222, Dowling notes, "A well-established but curious observation is that older long-term memories are more persistent in many forms of brain disease than are more recent memories." This fact is actually inconsistent with claims that memories are stored in brains. We know that the proteins that make up synapses have average lifetimes of only a few weeks, and that the synapses themselves are subject to spontaneous remodeling that makes them unstable. Given such realities, if memories were stored in brains, the ones that you would lose first are the oldest memories, since there would be so much more time for such memories to physically deteriorate. Similarly, if words were written on leaves, the older the writing was, the smaller the chance that it would survive.
Dowling says on page 222, "It would appear that long-term memories are not permanently stored in the hippocampus but transferred elsewhere, probably various regions of the cortex." He gives no data backing up this claim, and there is no evidence for such memory transfer, nor does anyone have any idea of how it could work. Because there is so much signal noise in the brain, so much noise in synapses, and so much noise and unreliability in the synapses of the cortex in particular, it is not credible that accurate memory information could move from the hippocampus to the cortex. A scientific paper says, "In the cortex, individual synapses seem to be extremely unreliable: the probability of transmitter release in response to a single action potential can be as low as 0.1 or lower." Signal transmission in the cortex would require the traversal of many synapses, and in each of these traversals there would be a low likelihood of a successful transmission of the signal. This unreliability of signal transmission in the cortex would be equivalent to signal noise even greater than we see in the bottom diagram, making it impossible for precise memories to transfer from the hippocampus to the cortex (and also making it impossible to precisely recall a detailed memory from the cortex).
We know that in hemispherectomy operations in which half of a brain is removed to stop epileptic seizures, there is little damage to memory, even though half of the cortex is surgically removed. Another reason for rejecting the idea of memories transferring from the hippocampus to the cortex is the issue of what can be called signal drowning. Signal drowning is what happens when there are so many signals from so many sources that a particular signal is effectively drowned out. Such signal drowning would occur in a malfunctioning television which showed the signal from every cable TV channel all at once, or a malfunctioning radio which played simultaneously the music and words from every AM station at the same time. It would seem that in the cortex there would have to be exactly such signal drowning, because each neuron emits a signal very frequently (about once per second or more), and each neuron is connected directly to more than a thousand other neurons. So we can't imagine how the cortex could receive a memory transferred from the hippocampus, as such a signal would get drowned out from all the random signals from other neurons emitting so frequently.
Facts such as the low cognitive impact of surgical removal of half of the brain, the huge amount of noise in the brain and synapses, the unreliable transmission of synapses, and the short lifetimes of the proteins that make up synapses are examples of very important neuroscience facts (with huge implications) that neuroscientists such as Dowling avoid mentioning in their books, for they do not wish to discuss observations contrary to their dogmatic claims.
Dowling has several pages discussing what is called LTP, trying to make it sound like this short-term effect (produced by artificial methods) has some relevance to memory. Despite all of the "busy work" time neuroscientists have spent on LTP, no scientist has shown that is has any relevance to memory. We know that despite its misleading name (LTP stands for long-term potentiation), LTP is actually a very short-lived affair, almost always lasting less than a few days. So such a thing cannot account for memories that last for 50 years.
Like some student who knows nothing about the origin of World War I saying, "I don't exactly understand that," Dowling confesses on page 222, "Exactly how memories are stored in neurons or in neuronal circuits remains a mystery." But why would that be, if memories were actually stored in neurons? We discovered exactly how genetic information is stored in the nucleus of the cell around 1953. Is it really credible that 66 years later we would still have no understanding of how memories are stored in the brain, if they actually were stored in the brain? No, it isn't. What is far more credible is that memories are not stored in brains, and that is exactly why no one has been able to read a memory from a bit of brain tissue in a lab, even though it is 66 years after laboratory scientists were able to read genetic information from inside cells.
No comments:
Post a Comment