Processing of primary and secondary rewards: A quantitative meta-analysis and review of human functional neuroimaging studies

One fundamental question concerning brain reward mechanisms is to determine how reward-related activity is influenced by the nature of rewards. Here, we review the neuroimaging literature and explicitly assess to what extent the representations of primary and secondary rewards overlap in the human brain. To achieve this goal, we performed an activation likelihood estimation (ALE) meta-analysis of 87 studies (1452 subjects) comparing the brain responses to monetary, erotic and food reward outcomes. Those three rewards robustly engaged a common brain network including the ventromedial prefrontal cortex, ventral striatum, amygdala, anterior insula and mediodorsal thalamus, although with some variations in the intensity and location of peak activity. Money-specific responses were further observed in the most anterior portion of the orbitofrontal cortex, supporting the idea that abstract secondary rewards are represented in evolutionary more recent brain regions. In contrast, food and erotic (i.e. primary) rewards were more strongly represented in the anterior insula, while erotic stimuli elicited particularly robust responses in the amygdala. Together, these results indicate that the computation of experienced reward value does not only recruit a core "reward system" but also reward type-dependent brain structures

The Impact of Motivation on Object-Based Visual Attention Indexed by Continuous Flash Suppression.

Motivationally-relevant stimuli summon our attention and benefit from enhanced processing, but the neural mechanisms underlying this prioritization are not well understood. Using an interocular suppression technique and functional neuroimaging, this work has the ultimate aim of understanding how motivation impacts visual perception. In Chapter 2a, we demonstrate that novel objects with a more rich reward history are prioritized in awareness more quickly than objects with a lean reward history. In Chapter 2b, we show that faces are prioritized in awareness following social rejection, and that the amount faces are prioritized correlates with individual differences in social motivation. Chapters 3 & 4 use a combination of functional neuroimaging and flash suppression to suppress fearful faces and houses from awareness. Using binocular rivalry and motion flash suppression in Chapter 3, we find that suppressed fearful faces activate the amygdala relative to suppressed houses, and the amygdala increases coherence with a network of regions involved in attention, including bilateral pulvinar, bilateral insula, left frontal eye fields, left inferior parietal cortex, and early visual cortex. Using the more robust technique, continuous flash suppression, in Chapter 4, we find no differentiation between stimuli based on mean amygdala responses. However, we show increased connectivity between the amygdala, the pulvinar, and inferior parietal cortex specific to fearful faces. Overall, these results indicate that motivationally-relevant stimuli activate the amygdala prior to awareness. Enhanced connectivity between the amygdala and regions involved in attention may underlie the enhanced processing seen for salient stimuli

The song system of the human brain.

Although sophisticated insights have been gained into the neurobiology of singing in songbirds, little comparable knowledge exists for humans, the most complex singers in nature. Human song complexity is evidenced by the capacity to generate both richly structured melodies and coordinated multi-part harmonizations. The present study aimed to elucidate this multi-faceted vocal system by using 15O-water positron emission tomography to scan ?listen and respond? performances of amateur musicians either singing repetitions of novel melodies, singing harmonizations with novel melodies, or vocalizing monotonically. Overall, major blood flow increases were seen in the primary and secondary auditory cortices, primary motor cortex, frontal operculum, supplementary motor area, insula, posterior cerebellum, and basal ganglia. Melody repetition and harmonization produced highly similar patterns of activation. However, whereas all three tasks activated secondary auditory cortex (posterior Brodmann Area 22), only melody repetition and harmonization activated the planum polare (BA 38). This result implies that BA 38 is responsible for an even higher level of musical processing than BA 22. Finally, all three of these ?listen and respond? tasks activated the frontal operculum (Broca's area), a region involved in cognitive/motor sequence production and imitation, thereby implicating it in musical imitation and vocal learning

Naturalistic language comprehension : a fMRI study on semantics in a narrative context

Semantiikka tutkii kieleen sisältyviä merkityksiä, joita tarvitaan kielen ymmärryksessä. Kuinka aivomme käsittelevät semantiikkaa ja kuinka ymmärrämme erityisesti luonnollisessa muodossa olevaa kieltä, on vielä aivotutkijoille epäselvää. Tässä tutkimuksessa kysyttiin, miten laajemmassa kontekstissa, narratiivissa, olevan kielen ymmärrys ja semanttinen prosessointi heijastuu aivojen aktiivisuuteen. Koehenkilöt kuulivat narratiivin toiminnallisen magneettiresonanssikuvantamisen (fMRI) aikana. Narratiivin semanttinen sisältö mallinnettiin laskennallisesti word2vec algoritmin avulla, ja tätä mallia verrattiin veren happitasosta riippuvaiseen (BOLD) aivosignaaliin ridge regression avulla vokseli kerrallaan. Lähestymistavalla saatiin eristettyä yksityiskohtaisempaa tietoa jatkuvan stimuluksen aivodatasta perustuen kielen semanttiseen sisältöön. Subjektien välinen BOLD-signaalin korrelaatio (ISC) itsessään paljasti molempien aivopuoliskojen osallistuvan kielen ymmärrykseen laajasti. Alueellista päällekkäisyyttä löytyi muiden aivoverkostojen kanssa, jotka vastaavat mm. mentalisaatiosta, muistista ja keskittymiskyvystä, mikä viittaa kielen ymmärryksen vaativan myös muiden kognition osien toimintaa. Ridge regression tulokset viittaavat bilateraalisten pikkuaivojen, superiorisen, keskimmäisen sekä mediaalisen etuaivokuoren poimujen, inferiorisen ja mediaalisen parietaalikuoren sekä visuaalikuoren, sekä oikean temporaalikuoren osallistuvan narratiivin semanttiseen prosessointiin aivoissa. Aiempi semantiikan tutkimus on tuottanut samankaltaisia tuloksia, joten word2vec vaikuttaisi tämän tutkimuksen perusteella mallintavan semantiikkaa riittävän hyvin aivotutkimuksen tarpeisiin. Tutkimuksen perusteella molemmat aivopuoliskot osallistuvat kielen laajemman kontekstin käsittelyyn, ja semantiikka nähdään aktivaationa eri puolilla aivokuorta. Nämä aktiivisuudet ovat mahdollisesti riippuvaisia kielen sisällöstä, mutta miten paljon kielen sisältö vaikuttaa eri aivoalueiden osallistumiseen kielen semanttisessa prosessoinnissa, on vielä avoin tutkimuskysymys.Semantics is a study of meaning in language and basis for language comprehension. How these phenomena are processed in the brain is still unclear especially in naturalistic context. In this study, naturalistic language comprehension, and how semantic processing in a narrative context is reflected in brain activity were investigated. Subjects were measured with functional magnetic resonance imaging (fMRI) while listening to a narrative. The semantic content of the narrative was modelled computationally with word2vec and compared to voxel-wise blood-oxygen-level dependent (BOLD) brain signal time courses using ridge regression. This approach provides a novel way to extract more detailed information from the brain data based on semantic content of the stimulus. Inter-subject correlation (ISC) of voxel-wise BOLD signals alone showed both hemispheres taking part in language comprehension. Areas involved in this task overlapped with networks of mentalisation, memory and attention suggesting comprehension requiring other modalities of cognition for its function. Ridge regression suggested cerebellum, superior, middle and medial frontal, inferior and medial parietal and visual cortices bilaterally and temporal cortex on right hemisphere having a role in semantic processing of the narrative. As similar results have been found in previous research on semantics, word2vec appears to model semantics sufficiently and is an applicable tool in brain research. This study suggests contextual language recruiting brain areas in both hemispheres and semantic processing showing as distributed activity on the cortex. This activity is likely dependent on the content of language, but further studies are required to distinguish how strongly brain activity is affected by different semantic contents

Principal Component Analysis

This book is aimed at raising awareness of researchers, scientists and engineers on the benefits of Principal Component Analysis (PCA) in data analysis. In this book, the reader will find the applications of PCA in fields such as taxonomy, biology, pharmacy,finance, agriculture, ecology, health and architecture