From anatomy to function: the role of the somatosensory cortex in emotional regulation

Since the pioneering work of Penfield and his colleagues in the 1930s, the somatosensory cortex, which is located on the postcentral gyrus, has been known for its central role in processing sensory information from various parts of the body. More recently, a converging body of literature has shown that the somatosensory cortex also plays an important role in each stage of emotional processing, including identification of emotional significance in a stimulus, generation of emotional states, and regulation of emotion. Importantly, studies conducted in individuals suffering from mental disorders associated with abnormal emotional regulation, such as major depression, bipolar disorder, schizophrenia, post-traumatic stress disorder, anxiety and panic disorders, specific phobia, obesity, and obsessive-compulsive disorder, have found structural and functional changes in the somatosensory cortex. Common observations in the somatosensory cortices of individuals with mood disorders include alterations in gray matter volume, cortical thickness, abnormal functional connectivity with other brain regions, and changes in metabolic rates. These findings support the hypothesis that the somatosensory cortex may be a treatment target for certain mental disorders. In this review, we discuss the anatomy, connectivity, and functions of the somatosensory cortex, with a focus on its role in emotional regulation.

Morphometric analysis of feedforward pathways from the primary somatosensory area (S1) of rats

We used biotinylated dextran amine (BDA) to anterogradely label individual axons projecting from primary somatosensory cortex (S1) to four different cortical areas in rats. A major goal was to determine whether axon terminals in these target areas shared morphometric similarities based on the shape of individual terminal arbors and the density of two bouton types: en passant (Bp) and terminaux (Bt). Evidence from tridimensional reconstructions of isolated axon terminal fragments (n=111) did support a degree of morphological heterogeneity establishing two broad groups of axon terminals. Morphological parameters associated with the complexity of terminal arbors and the proportion of beaded Bp vs stalked Bt were found to differ significantly in these two groups following a discriminant function statistical analysis across axon fragments. Interestingly, both groups occurred in all four target areas, possibly consistent with a commonality of presynaptic processing of tactile information. These findings lay the ground for additional work aiming to investigate synaptic function at the single bouton level and see how this might be associated with emerging properties in postsynaptic targets.

Alpha power oscillation in the frontal cortex under Bromazepam and Modafinil effects / Oscilações da potência alfa no córtex frontal sob influência do Bromazepam e Modafinil

ABSTRACTObjective Our aim was to investigate and compare the neuromodulatory effects of bromazepam (6 mg) and modafinil (200 mg) during a sensorimotor task analyzing the changes produced in the absolute alpha power.Method The sample was composed of 15 healthy individuals exposed to three experimental conditions: placebo, modafinil and bromazepam. EEG data were recorded before, during and after the execution of the task. A three-way ANOVA was applied, in order to compare the absolute alpha power among the factors: Group (control, bromazepam and modafinil) Condition (Pre and Post-drug ingestion) and Moment (pre and post-stimulus).Results Interaction was found between the group and condition factors for Fp1, F4 and F3. We observed a main effect of moment and condition for the Fp2, F8 and Fz electrodes.Conclusion We concluded that drugs may interfere in sensorimotor processes, such as in the performance of tasks carried out in an unpredictable scenario.

RESUMOObjetivo Investigar e comparar os efeitos neuromoduladores do bromazepam (6mg) e modafinil (200mg), durante a prática de uma tarefa sensoriomotora, analisando as modificações produzidas na potência absoluta de alfa.Método A amostra foi composta por 15 indivíduos saudáveis, expostos a três condições experimentais: Placebo, modafinil e bromazepam. Dados eletroencefalográficos foram registrados antes, durante e após a execução da tarefa motora. Um ANOVA three-way foi aplicado para comparar a potência absoluta de alfa nos fatores Grupo (controle, bromazepam e modafinil), Condição (Pré e Pós ingestão da droga) e Momento (Pré e Pós estimulo).Resultados Verificou-se interação entre os fatores grupo e condição para os eletrodos Fp1, F4 e F3. Observamos um efeito principal para momento e condição nos eletrodos Fp2, F8 e Fz.Conclusão Concluímos que as drogas, podem interferir em processos sensoriomotores, como no desempenho de tarefas executadas em um cenário imprevisível.

The effects of bromazepam over the central and frontal areas during a motor task: an EEG study / Os efeitos do bromazepam nas áreas corticais central e frontal durante execução de uma tarefa motora: um estudo de EEG

The present study investigates the influence of bromazepam while executing a motor task. Specifically, we intend to analyze the changes in alpha absolute power under two experimental conditions, bromazepam and placebo. We also included analyses of theta and beta frequencies. We collected electroencephalographic data before, during, and after motor task execution. We used a Two Way ANOVA to investigate the condition (PL × Br6 mg) and moment (pre and post) variables for the following electrodes: Fp1, Fp2, F7, F3, Fz, F4, F8, C3, CZ and C4. We found a main effect for condition on the electrodes FP1, F7, F3, Fz, F4, C3 and CZ, for alpha and beta bands. For beta band we also found a main effect for condition on the electrodes Fp2, F8 and C4; for theta band we identified a main effect for condition on C3, Cz and C4 electrodes. This finding suggests that the motor task did not have any influence on the electrocortical activity in alpha, and that the existing modifications were a consequence due merely to the drug use. Despite its anxiolytic and sedative action, bromazepam did not show any significant changes when the individuals executed a finger extension motor task.

O presente estudo investiga a influência do bromazepam durante a execução de uma tarefa motora. Especificamente, pretende-se analisar as mudanças na potência absoluta de alfa sob duas condições experimentais, bromazepam e placebo. Nós também incluímos as analises das frequências teta e beta. Foram coletados dados eletroencefalográficos antes, durante e depois da execução da tarefa motora. Usamos uma Anova de 2 fatores para investigar a condição (PL × Br6 mg) e variáveis no momento (pré e pós) para os seguintes eletrodos: Fp1, Fp2, F7, F3, Fz, F4, F8, C3, C4 e CZ. Encontramos um efeito principal para a condição e eletrodos FP1, F7, F3, Fz, F4, C3 e CZ para alfa e beta. Para beta também foi encontrado um efeito principal para condição nos eletrodos Fp2, F8 e C4; para theta nós identificamos um efeito principal para condition em C3, Cz e C4. Este achado sugere que a tarefa motora não tem qualquer influência sobre a atividade eletrocortical alfa e que as modificações existentes foram uma consequência devido o uso de drogas. Apesar de sua ação ansiolítica e sedativa, o bromazepam não apresentou mudança significativa quando os indivíduos executaram uma tarefa motora.

Plasticity in primary somatosensory cortex resulting from environmentally enriched stimulation and sensory discrimination training

We studied primary-somatosensory cortical plasticity due to selective stimulation of the sensory periphery by two procedures of active exploration in adult rats. Subjects, left with only three adjacent whiskers, were trained in a roughness discrimination task or maintained in a tactile enriched environment. Either training or enrichment produced 3-fold increases in the barrel cortex areas of behaviorally-engaged whisker representations, in their zones of overlap. While the overall areas of representation expanded dramatically, the domains of exclusive principal whisker responses were virtually identical in enriched vs normal rats and were significantly smaller than either group in roughness discrimination-trained rats. When animals were trained or exposed to enriched environments with the three whiskers arrayed in an are or row, very equivalent overlaps in representations were recorded across their greatly-enlarged whisker representation zones. This equivalence in distortion in these behavioral preparations is in contradistinction to the normal rat, where overlap is strongly biased only along rows, probably reflecting the establishment of different relations with the neighboring cortical columns. Overall, plasticity phenomena are argued to be consistent with the predictions of competitive Hebbian network plasticity.

Non-homogeneous spatial configuration of vibrissae cortical representation in layer IV of the barrel somatosensory cortex

In the present experiments we studied exclusive and overlapping cortical representational areas of the vibrissae in layer IV cells, across the entire barrel subfield of the rat somatosensory cortex, looking for evidences that would challenge the present assumptions of homogeneity and symmetry among cortical columns in this sensorial system. Our main findings were that in layer IV of the rat barrel cortex: A) Size of vibrissae cortical representational areas (X=0.4174mm²; SD=0.025) was not homo geneous, vibrissae in dorsal rows (A-B) had significantly smaller areas than those in ventral rows (D-E), a pattern that repeated itself in arcs 1-4. B) This difference arises from vibrissal representational overlap, and not from variations in exclusive zones, which are surprisingly homogeneous in size across the barrel cortex (X=0.079mm²; SD=0.0075); C) The extent of overlapping cortical areas varied systematically, with intra-row overlapping areas having a predominant bias (71.4 percent of total overlapping) independent of area sizes. Accordingly, vibrissae shared receptive fields with an average of 1.15 vibrissae in the same row and 0.38 in the same are. Barrel cortex has been viewed operationally as a conglomerate of essentially homogenous cortical columns that interact equivalently in the are and row dimensions. Our simple but global cortical reconstructions show that this predominant view should be revised. We postulate that the vibrissae/barrels spatial disposition in rows and ares has a relevant functional meaning, related to different sensory capabilities.

Magnetoencephalogram recording from secondary motor areas during imagined movements

Este estudo determina se a atividade motora secundária cortical (M2) pode ser gravada durante simulação interna do movimento (IM) das mãos direita e esquerda utilizando-se magnetencefalografia (MEG). Os resultados da simulação dos movimentos estudados foram comparados com um ensaio somato-sensorial com estimulação tactil passiva em um sujeito. Durante o ensaio somato-sensorial dipolos foram detectados em áreas somato-sensoriais (SS) e motoras primarias (MI) tendo como score 94,4-98,4% para SS, 1,6-5,6% para M1 e 0% para M2. Durante o ensaio de simulação dos movimentos também foram detectados dipolos em SS 61,1-68,8%, M1 2,6-9,3% e M2 28,6-29,6%. Estes dados evidenciam a hipótese de que as áreas M2 são ativadas durante a simulação dos movimentos das mãos. Este estudo sugere o desenvolvimento de um teste diagnóstico para pacientes com deficites motores, que avalie a rede somatomotora com interesse específico nas áreas M2.

Environmental enrichment during early postnatal development decreases parvalbumin expression in the rat somatosensory cortex

In the rat brain, parvalbumin (PV) expression starts on postnatal day 8 and comprises a heterogeneous population of nonpyramidal GABAergic neurons. In the present work, an immunohistochemical study was done on control and experimental rats submitted to enriched environmental conditions between postnatal days 3 to 18 or 3 to 24. Counts of PV+ neurons were made in the dorsomedial and in the ventrolateral regions of the somatosensory cortex. In control animals, PV+ neurons reached a peak on day 24 declining towards day 120. In these rats a peculiar distribution pattern was detected in which immunoreactive neurons are more numerous in the dorsomedial than ventrolateral regions as well in infragranular than supragranular layers and in posterior regions than anterior ones. Differences observed in these three dimensions were well established on day 24. Rats exposed to the enriched environment from day 3 to day 24 show a reduction (26 por ciento) in the number of PV+ neurons. The effects of the enrichment persisted for at least 12 days since animals submitted to the enriched condition from day 3 to day 18 and sacrificed on day 30 present a similar reduction (29 por ciento) in the number of PV immunoreactive neurons. Environmental enrichment induces a significant reduction of PV+ neurons but the overall distribution is retained. This finding suggests some degree of stability in the expression of PV in the rat somatosensory cortex.

Beyond maps: a dynamic view of the somatosensory system

Current theories on how tactile information is processed by the mammalian somatosensory system are based primarily on data obtained in studies in which the physiological properties of single neurons were characterized, one at a time, in behaving or anesthetized animals. Yet, the central nervous system relies on the concurrent activation of large populations of neurons to process the variety of sensory stimuli that contribute to normal tactile perception. The recent introduction of electrophysiological methods for chronic and simultaneous recordings of the extracellular activity of large numbers of single neurons per animal has allowed us to investigate, for the first time, how populations of neurons, located at multiple processing stages of the somatosensory system, interact following passive and active tactile stimulation. The rat trigeminal somatosensory system was used as a model for this investigation. Our results revealed the existence of highly dynamic and distributed representations of tactile information, not only in the somatosensory cortex, but also in the thalamus and even in the brainstem. In these structures, we identified broadly tuned neurons with multiwhisker receptive fields (RFs). In the thalamus, a large percentage of neurons exhibited shifts in the spatial domain of their RFs as a function of post-stimulus time. During these shifts, the center of the neuron's RF moved across the whisker pad from caudal to rostral whiskers, but not in the opposite direction, suggesting that these spatiotemporal RFs may encode directional information. Further studies revealed that somatosensory representations were maintained by dynamic interactions between multiple convergent afferents, since they could be altered in a matter of seconds by reversible sensory deprivations. Overall, these results suggest that the rat somatosensory system relies on both spatial and temporal interactions between populations of cortical and subcortical neurons to process multiple attributes of tactile stimuli.

Somatosensory evoked response: application in neurology.

Potencial evocado somato-sensorial (PES) por estimulacao eletrica do nervo mediano e a resposta eletrica produzida pela ativacao do plexo braquial, raizes C6-7, medula cervical, sistema lemniscal do tronco cerebral, talamo e cortex sensorial. Este teste clinico, nao invasivo, permite a avaliacao da integridade funcional da via somato-sensorial possibilitando a localizacao de lesoes nos niveis acima apontados. O PES tem sido util no estudo de comas, esclerose multipla, doencas vasculares e outras patologias do sistema nervoso.PES por estimulacao do nervo peroneiro parece ser muito sensivel na deteccao precoce do comprometimento da medula espinal