What is the Human Cortex?

The cerebral cortex is the thin surface layer of the brain found in vertebrate animals that has evolved most recently, showing the greatest variation in size among different mammals (it is especially large in humans). Each part of the cerebral cortex is six layered (e.g., L2), with different kinds of nerve cells (e.g., spiny stellate) in each layer. The cerebral cortex plays a crucial role in most higher level cognitive functions, such as thinking, memory, planning, perception, language, and attention. Although there has been some progress in understanding the macroscopic organization of this very complicated tissue, its organization at the level of individual nerve cells and their interconnecting synapses is largely unknown.

Petabyte connectomic reconstruction of a volume of human neocortex. Left: Small subvolume of the dataset. Right: A subgraph of 5000 neurons and excitatory (green) and inhibitory (red) connections in the dataset. The full graph (connectome) would be far too dense to visualize.

Mapping the structure of the brain at the resolution of individual synapses requires high-resolution microscopy techniques that can image biochemically stabilized (fixed) tissue. We collaborated with brain surgeons at Massachusetts General Hospital in Boston (MGH) who sometimes remove pieces of normal human cerebral cortex when performing a surgery to cure epilepsy in order to gain access to a site in the deeper brain where an epileptic seizure is being initiated. Patients anonymously donated this tissue, which is normally discarded, to our colleagues in the Lichtman lab. The Harvard researchers cut the tissue into ~5300 individual 30 nanometer sections using an automated tape collecting ultra-microtome, mounted those sections onto silicon wafers, and then imaged the brain tissue at 4 nm resolution in a customized 61-beam parallelized scanning electron microscope for rapid image acquisition.

Imaging the ~5300 physical sections produced 225 million individual 2D images. The team then computationally stitched and aligned this data to produce a single 3D volume. While the quality of the data was generally excellent, these alignment pipelines had to robustly handle a number of challenges, including imaging artifacts, missing sections, variation in microscope parameters, and physical stretching and compression of the tissue. Once aligned, a multiscale flood-filling network pipeline was applied (using thousands of Google Cloud TPUs) to produce a 3D segmentation of each individual cell in the tissue. Additional machine learning pipelines were applied to identify and characterize 130 million synapses, classify each 3D fragment into various “subcompartments” (e.g., axon, dendrite, or cell body), and identify other structures of interest such as myelin and cilia. Automated reconstruction results were imperfect, so manual efforts were used to “proofread” roughly one hundred cells in the data. Over time, the scientists expect to add additional cells to this verified set through additional manual efforts and further advances in automation.

Source: https://ai.googleblog.com/

AI Detects In Your Language Early Sign Of Alzheimer’s Disease

An artificial intelligence program analyzing language predicted whether people with no memory or thinking problems would develop Alzheimer’s disease later in life, researchers said. The study by IBM, funded by drug giant Pfizer, found a computerized model analyzing language patterns accurately predicted up to 74% of participants diagnosed with Alzheimer’s disease later in lifeEarly detection of Alzheimer’s disease is crucial, as the memory-robbing disease  afflicts about 5.8 million Americans.

Many researchers are working to develop blood tests to detect Alzheimer’s before memory and thinking problems occur. Blood tests can potentially be more precise than memory and cognitive tests now used to diagnose the disease. The tests also could be a less expensive way to conduct clinical studies.

IBM officials say their study of language patterns show another possible tool for early detection of Alzheimer’s disease and other forms of dementia. Ajay Royyuru, IBM’s vice president of health care and life sciences research, said IBM‘s research efforts to track language shows the potential for a noninvasive test that “presents a better window for targeted interventions.”

The research analyzed more than 700 written samples from 270 participants in the decades-old Framingham Heart Study, which has collected detailed medical histories, physical exams and lab tests from thousands of participants. Participants were shown a cookie-theft picture and asked to write a description of the image. The samples were collected when participants showed no signs of memory loss. The datas predicted Alzheimer’s disease an average of 7.6 years before participants were diagnosed.

The findings are reported in the journal EClinicalMedicine.

Source: https://www.ibm.com/
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https://eu.usatoday.com/

 

Genes Behind Humankind’s Big Brain

Scientists have pinpointed three genes that may have played a pivotal role in an important milestone in human evolution: the striking increase in brain size that facilitated cognitive advances that helped define what it means to be human. These genes, found only in people, appeared between 3 and 4 million years ago, just prior to a period when the fossil record demonstrates a dramatic brain enlargement in ancestral species in the human lineage, researchers said. The three nearly identical genes, as well as a fourth nonfunctional one, are called NOTCH2NL genes, arising from a gene family dating back hundreds of millions of years and heavily involved in embryonic development. 

The NOTCH2NL genes are particularly active in the reservoir of neural stem cells of the cerebral cortex, the brain’s outer layer responsible for the highest mental functions such as cognition, language, memory, reasoning and consciousness. The genes were found to delay development of cortical stem cells into neurons in the embryo, leading to the production of a higher number of mature nerve cells in this brain region.

The cerebral cortex defines to a large extent what we are as a species and who we are as individuals. Understanding how it emerged in evolution is a fascinating question, touching at the basic origins of mankind,” said developmental neurobiologist Pierre Vanderhaeghen of Université Libre de Bruxelles and VIB/KULeuven in Belgium.

It is the ultimate evolutionary question and it is thrilling to work in this area of research,” added biomolecular engineer David Haussler, scientific director of the University of California, Santa Cruz Genomics Institute and a Howard Hughes Medical Institute investigator.

Source: https://www.reuters.com/