Source: Evelina Fedorenko, Terri L. Scott, Peter Brunnerd, William G. Coon, Brianna Pritchett, Gerwin Schalk, and Nancy Kanwisher (2016): Neural correlate of the construction of sentence meaning. Proceedings of the National Academy of Sciences.

“How do circuits of neurons in your brain extract and hold the meaning of a sentence? To start to address this unanswered question, we measured neural activity from the surface of the human brain in patients being mapped out before neurosurgery, as they read sentences. In many electrodes, neural activity increased steadily over the course of the sentence, but the same was not found when participants read lists of words or pronounceable nonwords, or grammatical nonword strings (“Jabberwocky”). This build-up of neural activity appears to reflect neither word meaning nor syntax alone, but the representation of complex meanings.”

If there is something that unites linguists of all stripes it’s the recognition that, in some way or other, natural languages systematically represent the cognitive distinction between the agent and the theme or patient of an action. The distinction is known to play a crucial role in the representation of verb meanings and the way they semantically compose with the verb’s arguments. 

An article in the Harvard Gazette of October 5 reports that two neuroscientists at Harvard discovered that the brain represents agents and patients/themes of actions in two distinct adjacent regions. The experiments are beautiful. This would be an occasion for linguists to celebrate if it wasn’t for the fact that the finding is being reported as a discovery about how the brain builds new thoughts. I don’t know who is ultimately responsible for aggrandizing the nature of the finding. Already in the original article in the Proceedings of the National Academy of Sciences the reader is led to believe that what was found went beyond the mere neural localization of a well-established semantic distinction. At the beginning of the PNAS article, the significance of the reported findings is described as follows:

“The 18th-century Prussian philosopher Wilhelm von Humbolt famously noted that natural language makes “infinite use of finite means.” By this, he meant that language deploys a finite set of words to express an effectively infinite set of ideas. As the seat of both language and thought, the human brain must be capable of rapidly encoding the multitude of thoughts that a sentence could convey. How does this work? Here, we find evidence supporting a long-standing conjecture of cognitive science: that the human brain encodes the meanings of simple sentences much like a computer, with distinct neural populations representing answers to basic questions of meaning such as “Who did it?” and “To whom was it done?” “

The bulk of this paragraph  describes no less than the research program of modern linguistics. How can the National Academy of Sciences tolerate such a disconnect between two disciplines within the Cognitive Sciences? How is it possible that a paper in neuroscience describes as a sensational new finding something that amounts to no more than the localization in the brain of a well-known and well-researched semantic distinction? We’ll never make progress in Cognitive Science if we allow subdisciplines to ignore each other so as to increase the perceived importance of one’s own results. 

One quote (attributed to Steven Frankland) in the Harvard Gazette article may point to the source of the communication problem: “This [the systematic representation of agents and themes/patients, A.K.] has been a central theoretical discussion in cognitive science for a long time, and although it has seemed like a pretty good bet that the brain works this way, there’s been little direct empirical evidence for it.” This quote makes it appear as if the idea that the human mind systematically represents agents and themes/patients has had the mere status of a bet before the distinction could be actually localized in the brain. That the distinction is systematically represented in all languages of the world is not given the status of a fact in this quote – it doesn’t count as  “empirical evidence”. It’s like denying your pulse the status of a fact before we can localize the mechanisms that regulate it in the brain. 

Headlines are routinely used for false advertising in the Cognitive Sciences. Science should be immune to those practices. The reported finding concerns a tiny aspect of meaning composition of the most simple kind and it implies nothing about the exact mechanism of composition. There is no empirical basis for drawing grand conclusions about “how the brain builds new thoughts” or about the brain “architecture for encoding sentence meaning.” Exaggerated headlines should be on the list of unscholarly behaviors that journal editors might want to discourage. 

Sources: How the brain builds new thoughts (Harvard Gazette, October 8) and the September 15) issue of the Proceedings of the National Academy of Sciences: An architecture for encoding sentence meaning in left mid-superior temporal cortex.  

Source: MacArthur Foundation

We are born with an excess of synaptic connections. Through a normal developmental process called “pruning”, some of those synaptic connections get cut. Which ones? How are synaptic connections selected for elimination? What does all of this mean for our theories of how linguistic patterns and structures are acquired by children? 

“Beth Stevens is a neuroscientist whose research on microglial cells is prompting a significant shift in thinking about neuron communication in the healthy brain and the origins of adult neurological diseases. Until recently, it was believed that the primary function of microglia was immunological; they protected the brain by reducing inflammation and removing foreign bodies.

Stevens identified an additional, yet critical, role: the microglia are responsible for the “pruning” or removal of synaptic cells during brain development. Synapses form the connections, or means of communication, between nerve cells, and these pathways are the basis for all functions or jobs the brain performs. Using a novel model system that allows direct visualization of synapse pruning at various stages of brain development, Stevens demonstrated that the microglia’s pruning depends on the level of activity of neural pathways. She identified immune proteins called complement that “tag” (or bind) excess synapses with an “eat me” signal in the healthy developing brain. Through a process of phagocytosis, the microglia engulf or “eat” the synapses identified for elimination. This pruning optimizes the brain’s synaptic arrangements, ensuring that it has the most efficient wiring.”

Related articles: Microglia: New Roles for the Synaptic Stripper (Neuron) and Phagocytic cells: sculpting synaptic circuits in the developing nervous system.