The Chirurgeon’s Apprentice is a popular blog on the website of medical historian Dr Lindsey Fitzharris who received her doctorate from University of Oxford in medical, technology and science history. Dr Fitzharris discusses the apt naming of the blog with the word ‘chirurgeon‘ the first historical reference to a practitioner of surgery. The website illuminates the often grisly but fascinating historical developments in Medicine and Surgery with focus on the Victorian era and the rapidly developing techniques and methods occurring in all scientific disciplines at this time. Under the Knife is a well-researched and often darkly humorous video series delivered by Fitzharris where each episode details different aspects of the history of Surgery and Medicine. Dr Lindsey Fitzharris is also the author of a recent book The Butchering Art about the Victorian surgical pioneer Jospeh Lister and the development of antiseptic practices.
As we already discussed, small mammal species with short life spans and high metabolisms which experience seasonal fluctuation of resources tend to undergo seasonal changes in skull size and morphology. More recently, Lázaro et al. examined how this seasonal variation affected brain size and organization in the common shrew (Sorex araneus). They collected specimens in Southern Germany, covering all seasons and the whole lifespan of the shrew, which is about 18 months. The sample was divided into three age groups: summer juvenile, winter subadult, and spring-summer adult (sexually mature). Right hemispheres were used to investigate the volumes of the different brain regions, and the left hemispheres for examining neuron morphology. They confirmed the patterns of seasonal volume variation, and observed there were differences between brain regions and between sexes. The overall volume decrease from summer to winter was more pronounced in females, while spring regrowth was similar for both sexes, thus resulting in adult sexual dimorphism with females having smaller brain volumes. Regarding the brain regions, most significant changes were observed in the hypothalamus and the thalamus, both in the winter decrease and spring regrowth. Neocortex and striatum (mostly caudoputamen) volumes decreased in winter but did not regrow in spring. Cerebellar volumes were smaller in females during winter, but reached the same volumes as males during spring regrowth. According to the authors, as the volume reduction from juveniles to subadults occurs before winter, it is more likely genetically encoded than a direct result of temperature or resources fluctuation. Furthermore, the independent variation of the different brain regions suggests a mosaic adaptation of each structure to the cognitive requirements and energetic limitations of each season. Other explanations for the different patterns of variation between the different regions might be associated with differences in energetic demands and in the potential for plasticity between brain structures. However, the authors could not find correlations between seasonal volume changes and functional demands, developmental timing, or metabolic consumption of the different brain regions. They conclude the variation in each brain structure might be influenced by functional adaptations and plasticity to different degrees. The authors also registered the variation in neuron size and morphology in three regions. The caudoputamen showed a decline in dendritic length and volume, in soma size, and in spine number and density, from juvenile to adult. The somatosensory cortex displayed only decline in soma size from summer to winter and in spine density from winter to adult. In the anterior cingulate cortex there was a reduction in soma size from juvenile to adult but in dendrite volume only from juvenile to subadult. These results cannot explain adequately the observed volumetric changes in the respective regions, and other factors that might affect volume, such as the space between cells and neuron density, should be considered in further studies. Moreover, changes in axonal innervations and myelin, and in the density of microvessels should be considered as these can also influence energetic costs.
Studying the evolution of brain form requires paleoneruologists to rely on casts from the cranial cavity from fossil species. Due to the lack of soft-tissue preservation in fossils, descriptions of macroanatomy and cytoarchitecture are taken from comparative non-human primates to serve as hypothetical models of early hominin brain form. Using extant non-human primates as models for fossil species ignores the separation of lineages, any specific adaptations and lineage-specific evolution since divergence. Furthermore, extant species risk being relegated as ‘living fossils’ with the issue worsened by the absence of identifiable fossils for either Pan or Gorilla. The untenable assumption is that extant chimpanzee anatomy should resembles the original form prior to the Pan–Homo split. Nonetheless, comparison among living hominoids is still mandatory to investigate the evolutionary radiation of this taxon.
Previous published descriptions of chimpanzee sulcal patterns occur in classic literature but were based on only a few post-mortem dissections. Recently, Falk and colleagues aimed to increase knowledge of chimpanzee sulcal variation by describing sulcal patterns present in in-vivo Magnetic Resonance Imaging (MRI) from eight chimpanzees. Results suggested that, contrary to previous opinion, two sulci do occur in both chimpanzees and humans. To elaborate, these two sulci are the middle-frontal sulcus located in the frontal lobe, and lunate sulcus located between the parietal and occipital lobes.
No quantitative analyses were conducted in this study, but Falk et al. (2018) provide detailed descriptions of the variation between individuals, highlighting why descriptions based on only one or two individuals cannot be used to reliably describe the brain anatomy of a species. The authors argue the presence of the middle-frontal sulcus and lunate sulcus in chimpanzees invalidates previous claims that these sulci represent derived states found only in the human lineage. Further quantitative analyses with much larger samples, including both extant and fossil species will aid in a better understanding of the brain anatomy of humans and other great ape species.
Two different papers have been published this month on the evolution of the supraorbital anatomy in humans. The first article is on Neanderthal facial morphology, and it was coordinated by Stephen Wroe, of the FEAR lab. Here a comment on the Daily Mail. The second article, by Ricardo Miguel Godinho and coauthors, links supraorbital morphology and social dynamics, and it was commented in a News and Views by Markus Bastir.
Primates are unique among mammals for having a brain much larger than expected for body size. An important aim in paleoneurology is understanding how cerebral structures reorganized to accomodate primate cerebral expansion. The brain comprises only soft-tissue and does not fossilize so paleoneurologists rely on endocasts, either physical or digital molds of the cranial cavity, to estimate the macro-anatomy of the brain. Continuing computational advances and powerful imaging techniques have allowed the generation of increasingly higher-resolution digital endocasts. Gonzales et al. (2015) generated a high-resolution endocast of the 15 Myr-old fossil cercopithecine Victoriapithecus macinnesi using micro-CT scans. By using computational methods, taphonomic distortion was corrected and a new endocranial volume (ECV) of 35.6 cm3 reported for Victoriapithecus which is much smaller than the previous value 54 cm3. This new, smaller ECV places Victoriapithecus within the range of extant strepsirrhines but outside the range expected of extant and fossil cercopithecoids including the 32 Myr-old fossil species Aegyptopithecus zeuxis which had an ECV within the expected range for fossil cercopithecoids.
Despite Victoriapithecus exhibiting a very small ECV and falling below the range for extant cercopithecoids, the fossil does exhibit the ‘frog-shaped’ sulcal pattern shared only among cercopithecines. This sulcal pattern suggests Victoriapithecus is a cercopithecine, the ‘frog-shaped’ sulcal pattern is such a diagnostic trait that it is not shared by the leaf-eating colobines but only present in cercopithecines. The olfactory bulbs in Victoriapithecus are unusually large relative to the small ECV. Large olfactory bulbs are present in extant strepsirrhines and the fossil catarrhine Aegyptopithecus zeuxis but reduced in all extant and fossil cercopithecoids and hominoids. The presence of small olfactory bulbs in the 18 Myr-old hominoid Proconsul versus the large bulbs in Victoriapithecus suggested olfactory bulb reduction may have evolved independently in both cercopithecoids and hominoids.
Harrington et al. (2016) compared digital endocasts generated from micro-CT of three adapiform fossil primates including the 48 Myr-old Notharctus tenebrosus, 47 Myr-old Smilodectes gracilis and 45 Myr-old Adapis parisiensis. Results of endocranial volume (ECV) were consistent with other studies revealing an ECV of 7.6 cm3 for Notharctus, an ECV of 8.3 cm3 for Smilodectes while Adapis had an ECV of 8.8 cm3. The sulcal morphology of these adapiforms was also consistent with previous studies showing the defining feature of the primate brain, the Sylvian sulcus, is species-specific in these adapiforms. The Sylvian sulcus is well-defined in Adapis, occurs only as a shallow depression in Notharctus but is entirely lacking in Smilodectes. The absence of the Sylvian sulcus in Smilodectes is not understood but as it is absent in other mammals, this may represent a retained ancestral trait from before the divergence of primates from other mammals.
The cerebral organization of Notharctus and Smilodectes showed both possessed larger temporal and occipital lobes relative to brain size with smaller olfactory bulbs and frontal lobes. This trend might indicate cerebral reorganization favoring larger visual-auditory structures located in the temporal-occipital regions of the brain versus smaller visual-olfactory structures in the frontal region. The olfactory bulbs of these adapiforms were small and blunt relative to endocranial volume and predicted body mass but uniquely, Adapis parisiensis had the largest olfactory bulbs, placing it within the range of extant strepsirrhines. These studies reveal how little is understood about primate paleoneurology and the evolutionary trends of different primate lineages with implications for the human fossil record.
Visiting Peter Dockery and the amazing facilities of the brand new Human Biology Building at the National University of Ireland, Galway …
The journal of mammal zoology Hystrix has a new format and webpage. Here that good old 2013 volume on
Virtual Morphology and Evolutionary Morphometrics …
Intracranial infections represent serious brain diseases that occur in various forms and often may be hard to recognize in their earlier stages. A fast diagnosis is crucial for an effective treatment. Various technique of CT and MRI imaging have been developed to distinguish the symptoms in the brain and its associated tissues (see for example Hsu 2010). Radiologists recognize several categories of infections according to the origin (e.g. congenital and neonatal), location (intra-axial, extra-axial), or characters. In general, infections of the brain parenchyma, meninges and ventricles can have bacterial, viral, fungal, or parasitic origins. Bacterial infections usually develop from early cerebritis (inflammation of the cerebrum) to formation of abscesses (accumulation of infectious material and microorganisms) within the cranium. Some bacteria have more specific effects. Streptococcus pneumonia and Neisseria meningitides are common cause of bacterial meningitis (inflammation of the meninges and the cerebrospinal fluid). Tuberculomas, abscesses and tuberculous meningitis indicate presence of Mycobacterium tuberculosis (TB). Frequent viral infections are Herpes Simplex Encephalopathy involving Herpes simplex virus 1 (HSV-1), or infections induced by Human Immunodeficiency Virus (HIV) leading to cerebral atrophy and white matter disease. Fungal infections usually generate abscesses filled with fungi. Cryptococcosis and fungal meningitis are frequent fungal infections in some specific geographical regions. Examples of parasites causing intracranial infections are Toxoplasma gondii, or Taenia solium causing cysticercosis, which also leads to acquired epilepsy (see Vaccha et al. 2016). Consequences of intracranial infections could be in some cases lethal, in other cases they can cause a severe damage. For instance, infections of meninges and cerebrospinal fluid leading to meningitis can further evolve into subdural (between the dura mater and the underlying arachnoid layers) and epidural (between the meninges and the bone) abscesses, hydrocephalus (excessive accumulation of fluid in the brain), ventriculitis (inflammation of the ventricles containing and circulating cerebrospinal fluid throughout the brain), and venous thrombosis. Brain infection can be extended into the bone tissue and cause cranial pathologies like osteomyelitis or mastoiditis. Sometimes the infections can even lead to bone fractures. The origin of brain infection is often associated with traumas, when the microorganism spread from the wound into the soft tissues of the endocranium.