Electrophysiological correlates of dispositional mindfulness: A quantitative and complexity EEG study

While growing evidence supports that dispositional mindfulness relates to psychological health and cognitive enhancement, to date there have been only a few attempts to characterize its neural underpinnings. In the present study, we aimed at exploring the electrophysiological (EEG) signature of dispositional mindfulness using quantitative and complexity measures of EEG during resting state and while performing a learning task. Hundred twenty participants were assessed with the Five Facet Mindfulness Questionnaire and underwent 5 min eyes-closed resting state and 5 min at task EEG recording. We hypothesized that high mindfulness individuals would show patterns of brain activity related to (a) lower involvement of the default mode network (DMN) at rest (reduced frontal gamma power) and (b) a state of ‘task readiness’ reflected in a more similar pattern from rest to task (reduced overall q-EEG power at rest but not at task), as compared to their low mindfulness counterparts. Dispositional mindfulness was significantly linked to reduced frontal gamma power at rest and lower overall power during rest but not at task. In addition, we found a trend towards higher entropy during task performance in mindful individuals, which has recently been reported during mindfulness meditation. Altogether, our results add to those from expert meditators to show that high (dispositional) mindfulness seems to have a specific electrophysiological pattern characteristic of less involvement of the DMN and mind-wandering processes.     

Understanding complexity in the human brain

Although the ultimate aim of neuroscientific enquiry is to gain an understanding of the brain and how its workings relate to the mind, the majority of current efforts are largely focused on small questions using increasingly detailed data. However, it might be possible to successfully address the larger question of mind-brain mechanisms if the cumulative findings from these neuroscientific studies are coupled with complementary approaches from physics and philosophy. The brain, we argue, can be understood as a complex system or network, in which mental states emerge from the interaction between multiple physical and functional levels. Achieving further conceptual progress will crucially depend on broad-scale discussions regarding the properties of cognition and the tools that are currently available or must be developed in order to study mind-brain mechanisms.     

Understanding the dorsal and ventral systems of the human cerebral cortex: beyond dichotomies

Traditionally, characterizations of the macrolevel functional organization of the human cerebral cortex have focused on the left and right cerebral hemispheres. However, the idea of left brain versus right brain functions has been shown to be an oversimplification. We argue here that a top-bottom divide, rather than a left-right divide, is a more fruitful way to organize human cortical brain functions. However, current characterizations of the functions of the dorsal (top) and ventral (bottom) systems have rested on dichotomies, namely where versus what and how versus what. We propose that characterizing information-processing systems leads to a better macrolevel organization of cortical function; specifically, we hypothesize that the dorsal system is driven by expectations and processes sequences, relations, and movement, whereas the ventral system categorizes stimuli in parallel, focuses on individual events, and processes object properties (such as shape in vision and pitch in audition). To test this hypothesis, we reviewed over 100 relevant studies in the human neuroimaging and neuropsychological literatures and coded them relative to 11 variables, some of which characterized our hypothesis and some of which characterized the previous dichotomies. The results of forward stepwise logistic regressions supported our characterization of the 2 systems and showed that this model predicted the empirical findings better than either the traditional dichotomies or a left-right difference.     

Genetics of neuronal migration in the cerebral cortex

The development of the cerebral cortex requires large-scale movement of neurons from areas of proliferation to areas of differentiation and adult function in the cortex proper, and the patterns of this neuronal migration are surprisingly complex. The migration of neurons is affected by several naturally occurring genetic defects in humans and mice; identification of the genes responsible for some of these conditions has recently yielded new insights into the mechanisms that regulate migration. Other key genes have been identified via the creation of induced mutations that can also cause dramatic disorders of neuronal migration. However, our understanding of the physiological and biochemical links between these genes is still relatively spotty. A number of molecules have also been studied in mice (Reelin, mDab1, and the VLDL and ApoE2 receptors) that appear to represent part of a coherent signaling pathway that regulates migration, because multiple genes cause an indistinguishable phenotype when mutated. On the other hand, two human genes that cause lissencephaly (LIS1, DCX) encode proteins that have recently been implicated as regulators or microtubule dynamics. This article reviews some of the mutant phenotypes in light of the mechanisms of neuronal migration. MRDD Research Reviews 6:34-40, 2000.     

The brachium of the inferior colliculus: The human auditory pathways: A quantitative study

Counts of nerve fibers in the brachium of the inferior colliculus in man from birth to 97 years (28 brains) revealed an average on the right of 168,311/mm² and an average of 168,593/mm² on the left. The total fiber population for each level studied averaged 350,562 for section A (immediately adjacent to the inferior colliculus), 452, 372 for section B (center of brachium), and 559,242 for section C (immediately adjacent to the medial geniculate body). These figures were averaged from brains whose ages ranged from 11 to 89 years. The area of the brachium, as well as its total fiber population, increased as the medial geniculate body was approached. This indicates that fibers were entering the brachium at various points along its course from the inferior colliculus to the medial geniculate body or were leaving in the reverse direction. A lower fiber density was found in infant brains, and a loss of nerve fibers was evident in the 91- and the 97-year-old specimens.     

A short-term memory influence on the N1 response of cerebral cortex

The N1 component of auditory evoked potentials varies in amplitude as a function of the direction of attention and has been treated as a physiological correlate of stimulus set. Results from a sequential pitch memory experiment, presented here, show that N1 also indexes the strengths of short-term associations, suggesting that the N1 mechanism(s) may be involved in a more general process of organizing and/or maintaining temporary sensorimotor memories.     

Organization of short-term verbal memory in language areas of human cortex: Evidence from electrical stimulation

Short-term verbal memory (STVM) performance was measured during electrical stimulation of human left frontal-parietal-temporal cortex, at craniotomy under local anesthesia for the treatment of medically intractable epilepsy. The areas of cortex where stimulation alters language, as measured by object naming, are separate but adjacent to the areas where stimulation alters STVM. There are differential effects of stimulation during input, storage, and output phases of STVM at different cortical sites. These suggest that cortex adjacent to the posterior language area is a site of storage of STVM, while cortex adjacent to anterior language area is involved in retrieval from STVM.     

The human lateral lemniscus and its nuclei: The human auditory pathways: A quantitative study

Quantification of the human lateral lemniscus and its nuclei in 15 brains of patients without hearing impairment revealed these average values: Cross-sectional surface area of the bundle at the level of the nucleus of cranial nerve IV of 2.5 mm², fiber density of 77,000/mm²; 194,000 total fibers on each side; grouping of the nerve cells in three nuclei (olive remnant, ventral, and dorsal) the largest of which is the ventral; cell density in the olive remnant of 5009/mm³, in the ventral nucleus of 15,184/mm³, and 13,169 cells per mm³ in the dorsal nucleus; total cell populations in all nuclei of 20,063 on the left and 26,137 on the right; glial-neuronal index of 9.2; cell dimensions of 23.6 × 15.4 microns in the olive remnant and 21.2 × 12.2 in the other nuclei; combined nuclear volume of 1.91 mm³. Loss of neurons was not apparent in the aged brains but a significant reduction in counts of axons and in lemniscal bulk appeared in two of the older brains of the series (77 and 91 years).     

The cognitive significance of resonating neurons in the cerebral cortex

Most neural fibers of the cerebral cortex engage in electric signaling, but one particular fiber, the apical dendrite of the pyramidal neuron, specializes in electric resonating. This dendrite extends upward from somas of pyramidal neurons, the most numerous neurons of the cortex. The apical dendrite is embedded in a recurrent corticothalamic circuit that induces surges of electric current to move repeatedly down the dendrite. Narrow bandwidths of surge frequency (resonating) enable cortical circuits to use specific carrier frequencies, which isolate the processing of those circuits from other circuits. Resonating greatly enhances the intensity and duration of electrical activity of a neuron over a narrow frequency range, which underlies attention in its various modes. Within the minicolumn, separation of the central resonating circuit from the surrounding signal processing network separates “having” subjective impressions from “thinking about” them. Resonating neurons in the insular cortex apparently underlie cognitive impressions of feelings.     

A quantitative near-infrared spectroscopy study: a decrease in cerebral hemoglobin oxygenation in Alzheimer's disease and mild cognitive impairment

A newly developed quantitative near-infrared spectroscopy (NIRS) system was used to measure changes in cortical hemoglobin oxygenation during the Verbal Fluency Task in 32 healthy controls, 15 subjects with mild cognitive impairment (MCI), and 15 patients with Alzheimer's disease (AD). The amplitude of changes in the waveform, which was quantitatively calculated by a signal processing method, was significantly lower in the frontal, and the bilateral parietal areas in the AD group, whereas that in the MCI group was significantly lower only in the right parietal area. The NIRS system may be a potential tool for the primary screening of AD.     

A note on the gross configurations of the human auditory cortex

Gross inspection of 30 human brains (60 hemispheres) from patients without hearing impairment revealed the following configurations of gyri: one on left and two on right (14 of 30); two on left and two on right (11 of 30); one on left and one on right (3 of 30); two on left and one on right (1 of 30); and two on left and three on right (1 of 30). The last group has since been extended to include all combinations other than the first four and the proportions of these combinations appear to persist in larger tallies. Thirteen of the 30 brains displayed double gyri on the left while 25 had double gyri on the right. Seventeen of the 30 brains possessed a single gyrus on the left and four specimens had a single gyrus on the right. In general, the left side has a tendency to fewer gyral markings. The average cortical surface area on the left is 1198 mm² compared to 1380 on the right.     

A quantitative approach to the study of visual symmetry

An experiment was conducted to explore the quantitative relationship between "goodness" and the amount of symmetry in visual designs. Subjects arranged items in one, two, and three dimensions in an aesthetically pleasing manner. Each design was analyzed to determine its amount of symmetry, and the percent of subjects who created designs having each possible degree of asymmetry was calculated. Perfect symmetry was the most common condition for all three dimensions. Moreover, the goodness of patterns was inversely related to the quantitative degree of asymmetry.