Brodmann area | EPFL Graph Search

A Brodmann area is a region of the cerebral cortex, in the human or other primate brain, defined by its cytoarchitecture, or histological structure and organization of cells. The concept was first introduced by the German anatomist Korbinian Brodmann in the early 20th century. Brodmann mapped the human brain based on the varied cellular structure across the cortex and identified 52 distinct regions, which he numbered 1 to 52. These regions, or Brodmann areas, correspond with diverse functions including sensation, motor control, and cognition. History Brodmann areas were originally defined and numbered by the German anatomist Korbinian Brodmann based on the cytoarchitectural organization of neurons he observed in the cerebral cortex using the Nissl method of cell staining. Brodmann published his maps of cortical areas in humans, monkeys, and other species in 1909, along with many other findings and observations regarding the general cell types and laminar organization of t

Two-photon calcium imaging of neocortical projection neurons in whisker somatosensory cortex during goal-directed sensorimotor learning

Dimitra Angeliki Vavladeli

Abstract Excitatory projection neurons of the neocortex are thought to play important roles in per-ceptual and cognitive functions of the brain by directly connecting diverse cortical and subcortical areas. However, many aspects of the anatomical and functional organization of these inter-areal connections are unknown. The mouse primary somatosensory whisk-er barrel cortex (S1) serves as an important model for investigating the mammalian neo-cortex, and, here, I firstly investigate the structure and secondly the function of a specific subset of S1 cortico-cortical long-range projection neurons. In the first part of my thesis, I studied long-range axonal projections of excitatory layer 2/3 neurons with cell bodies located in S1. As a population, these neurons densely projected to secondary whisker somatosensory cortex (S2) and primary/secondary whisker motor cortex (M1/2), with additional axon in the dysgranular zone surrounding the barrel field, perirhinal temporal association cortex and striatum. The execution of a goal-directed behavior requires the brain to process incoming sensory information from the environment in a context-, learning- and motivation-dependent manner in order to perform specific motor actions. Cortico-cortical communica-tion in the context of goal-directed sensorimotor transformation has begun to be studied, but little is known about how signaling between interconnected cortical areas is modified by sensorimotor learning, as well as in response to changes in reward contingencies. Hence, in the second part of my thesis, I studied cortico-cortical dynamics in primary whisker somatosensory barrel cortex (S1) of mice during a combined whisker and audito-ry task. Using transgenic mice expressing GCaMP6f combined with two-photon micros-copy and retrograde labeling techniques, I chronically monitored the activity of excitatory layer 2/3 neurons in S1 projecting to M1 or S2, while mice learned the behavioral switch task. The results demonstrated that both classes of neurons responded after whisker and auditory stimulation. However, the whisker stimulus evoked response was stronger than the auditory stimulus evoked response. Neurons projecting to S2 exhibited stronger re-sponses compared to neurons projecting to M1 neurons. Those responses remained rela-tively stable across training sessions and under different reward conditions. Furthermore, both classes of neurons responded during spontaneous licking, but neurons projecting to S2 had larger licking-related responses compared to neurons projecting to M1. This work therefore furthers our knowledge of the structure and function of specific types of cortical projection neurons, which is a necessary step towards detailed under-standing of how sensory information might be signaled from primary sensory areas to downstream brain regions for further processing.

EPFL2018

Dopaminergic modulation of cortical motor network lateralization

Bogdan Draganski, Michael Herzog, Maya Anna Jastrzebowska, Renaud Marquis, Lester Melie Garcia

Introduction Unilateral movements are primarily processed in contralateral cortical and subcortical areas and additionally in ipsilateral cerebellum, leading to an asymmetric pattern of neural activation. Decrease of lateralization is characteristic of aging (Naccarato et al., 2006; Wu et al., 2005), and disease, for example, in unilateral brain lesions or stroke (Carr et al., 1993; Rehme et al., 2011) and Parkinson's disease (PD; Wu et al., 2015). The explanation for imbalanced lateralization in drug-naive PD is an adaptive compensation, compatible with the finding that PD-associated deficient input from cortico-subcortical circuits is compensated by reduced cortical inhibition and increased cortical facilitation (Blesa et al., 2017). Here, we investigated the effect of dopamine depletion and substitution on cortical motor lateralization, with the hypothesis that lateralization decreases in advanced PD and that administration of levodopa, at least to a certain extent, reinstates lateralization. Methods We used fMRI to study motor activation in advanced PD patients and in healthy controls (HC) during unilateral upper and lower limb movements. Ten right-handed, left side symptom-dominant PD patients were tested in pseudo-randomized order after intake of their usual dopaminergic medication – 'ON' state – and after withdrawal of medication – 'OFF' state. Eighteen right-handed age-matched HC participated in a single session. We quantified activation lateralization using the average laterality index (AveLI; Matsuo et al., 2012) in three cortical motor regions of interest (ROIs): primary motor cortex (M1), supplementary motor area (SMA) and premotor cortex (PMC), during the four movement conditions. We compared AveLI between group pairs (PD OFF vs. HC, PD ON vs. HC, PD OFF vs. PD ON) within each ROI and movement condition. We estimated the effective connectivity between ROIs using bilinear dynamic causal modeling (DCM; Friston et al., 2003) and developed a measure to quantify the lateralization of the resulting connectivity networks to compare between groups. By constructing a group level parametric empirical Bayes (PEB) model (Friston et al., 2016) over all the subjects and conducting a search over nested models, we compared DCM parameter estimates between groups, thus providing the potential link between changes in motor lateralization and connectivity. Results In line with our predictions, motor activation lateralization as estimated with the AveLI showed a trend towards decrease in the PD OFF group compared to HC, in all three ROIs during left hand movement and in M1 during left foot movement (Fig. 1). Between-group differences were observed solely in conditions corresponding to movement of the more affected body side. Contrary to our hypothesis, dopamine substitution did not reinstate lateralization – in fact, AveLI in the PD ON group closely resembled that of the PD OFF group. Connectivity lateralization of input-specific modulation (DCM.B) networks was significantly lower in all conditions in the PD group as compared to HC. While on the body side more affected by PD, differences were found for both PD OFF and PD ON, input-specific modulation related to the less affected side was more altered in PD ON. PEB analysis revealed qualitatively more between-group differences in input-specific modulation on the more affected PD side and included many interhemispheric connections (Fig. 2). Conclusions Decreased lateralization is not only present in drug-naïve PD patients (Wu et al., 2015) but also in dopa-treated patients. Acute dopamine modulation does not alter lateralization. Decreased lateralization is evident in both fMRI activation amplitudes (as estimated with AveLI) and effective connectivity (as demonstrated through the DCM analysis).

2018

Evolution amplified processing with temporally dispersed slow neuronal connectivity in primates

Hassan Ghaziri, Giorgio Innocenti

The corpus callosum (CC) provides the main route of communication between the 2 hemispheres of the brain. In monkeys, chimpanzees, and humans, callosal axons of distinct size interconnect functionally different cortical areas. Thinner axons in the genu and in the posterior body of the CC interconnect the prefrontal and parietal areas, respectively, and thicker axons in the midbody and in the splenium interconnect primary motor, somatosensory, and visual areas. At all locations, axon diameter, and hence its conduction velocity, increases slightly in the chimpanzee compared with the macaque because of an increased number of large axons but not between the chimpanzee and man. This, together with the longer connections in larger brains, doubles the expected conduction delays between the hemispheres, from macaque to man, and amplifies their range about 3-fold. These changes can have several consequences for cortical dynamics, particularly on the cycle of interhemispheric oscillators.

National Academy of Sciences2009