Hypothesized neural dynamics of working memory: several chunks might be marked simultaneously by harmonic frequencies within an octave band of brain waves

Ratio Indexes Based on Spectral Electroencephalographic Brainwaves for Assessment of Mental Involvement: A Systematic Review

BACKGROUND

This review systematically examined the scientific literature about electroencephalogram-derived ratio indexes used to assess human mental involvement, in order to deduce what they are, how they are defined and used, and what their best fields of application are. (2) Methods: The review was carried out according to the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. (3) Results: From the search query, 82 documents resulted. The majority (82%) were classified as related to mental strain, while 12% were classified as related to sensory and emotion aspects, and 6% to movement. The electroencephalographic electrode montage used was low-density in 13%, high-density in 6% and very-low-density in 81% of documents. The most used electrode positions for computation of involvement indexes were in the frontal and prefrontal cortex. Overall, 37 different formulations of involvement indexes were found. None of them could be directly related to a specific field of application. (4) Conclusions: Standardization in the definition of these indexes is missing, both in the considered frequency bands and in the exploited electrodes. Future research may focus on the development of indexes with a unique definition to monitor and characterize mental involvement.

The Musical Structure of Time in the Brain: Repetition, Rhythm, and Harmony in fMRI During Rest and Passive Movie Viewing

Space generally overshadows time in the construction of theories in cognitive neuroscience. In this paper, we pivot from the spatial axes to the temporal, analyzing fMRI image series to reveal structures in time rather than space. To determine affinities among global brain patterns at different times, core concepts in network analysis (derived from graph theory) were applied temporally, as relations among brain images at every time point during an fMRI scanning epoch. To explore the temporal structures observed through this adaptation of network analysis, data from 180 subjects in the Human Connectome Project were examined, during two experimental conditions: passive movie viewing and rest. The temporal brain, like the spatial brain, exhibits a modular structure, where "modules" are intermittent (distributed in time). These temporal entities are here referred to as themes. Short sequences of themes - motifs - were studied in sequences from 4 to 11 s in length. Many motifs repeated at constant intervals, and are therefore rhythmic; rhythms, converted to frequencies, were often harmonic. We speculate that the structure and interaction of these global oscillations underwrites the capacity to experience and navigate a world which is both recognizably stable and noticeably changing at every moment - a temporal world. In its temporal structure, this brain-constituted world resembles music.

A Hypothesis about the Biological Basis of Expert Intuition

It is well established that intuition plays an important role in experts’ decision making and thinking generally. However, the theories that have been developed at the cognitive level have limits in their explanatory power and lack detailed explanation of the underlying biological mechanisms. In this paper, we bridge this gap by proposing that Hebb's (1949) concept of cell assembly is the biological realization of Simon's (1974) concept of chunking. This view provides mechanisms at the biological level that are consistent with both biological and psychological findings. To further address the limits of previous theories, we introduce emotions as a component of intuition by showing how they modulate the perception-memory interaction. The idea that intuition lies at the crossroads between perception, knowledge, and emotional modulation sheds new light on the phenomena of expertise and intuition.

Music increases frontal EEG coherence during verbal learning

Anecdotal and some empirical evidence suggests that music can enhance learning and memory. However, the mechanisms by which music modulates the neural activity associated with learning and memory remain largely unexplored. We evaluated coherent frontal oscillations in the electroencephalogram (EEG) while subjects were engaged in a modified version of Rey's Auditory Verbal Learning Test (AVLT). Subjects heard either a spoken version of the AVLT or the conventional AVLT word list sung. Learning-related changes in coherence (LRCC) were measured by comparing the EEG during word encoding on correctly recalled trials to the immediately preceding trial on which the same word was not recalled. There were no significant changes in coherence associated with conventional verbal learning. However, musical verbal learning was associated with increased coherence within and between left and right frontal areas in theta, alpha, and gamma frequency bands. It is unlikely that the different patterns of LRCC reflect general performance differences; the groups exhibited similar learning performance. The results suggest that verbal learning with a musical template strengthens coherent oscillations in frontal cortical networks involved in verbal encoding.

Backward inhibition in a task of switching attention within verbal working memory

Three experiments were conducted to examine the backward inhibition effect in attention switching within verbal working memory. Experiment one showed significant backward inhibition effect in a "tri-count task". Experiment two suggested that the effect was not due to a perceptual inhibition on the previously presented figure. Experiment three excluded the sequential expectancy explanation for this inhibition effect. Our results suggest that attention switching between working memory items is accompanied by inhibition of the previously attended working memory item. The findings are discussed in respect to the account of the executive function.

On time, memory and dynamic form

A common approach to explaining the perception of form is through the use of static features. The weakness of this approach points naturally to dynamic definitions of form. Considering dynamical form, however, leads inevitably to the need to explain how events are perceived as time-extended--a problem with primacy over that even of qualia. Optic flow models, energy models, models reliant on a rigidity constraint are examined. The reliance of these models on the instantaneous specification of form at an instant, t, or across a series of such instants forces the consideration of the primary memory supporting both the perception of time-extended events and the time-extension of consciousness. This cannot be reduced to an integration over space and time. The difficulty of defining the basis for this memory is highlighted in considerations of dynamic form in relation to scales of time. Ultimately, the possibility is raised that psychology must follow physics in a more profound approach to time and motion.

Topology and graph theory applied to cortical anatomy may help explain working memory capacity for three or four simultaneous items

Cognitive experimentation suggests that at any single instant only three or four items ("chunks") are simultaneously prominent as a working memory (WM) trace, if we disregard the rehearsal component of WM. The reason for small WM capacity may concern combinatorial manageability. How might the neural representations of these few coactive chunks occupy a spatially distributed set of areas of the sheet-like cortex, while providing both order and flexibility to associate items in WM? Each attribute of each simultaneously active WM item must have broad access to the representational facilities of the cortical sheet, comprising tens of thousands of modular "cortical columns." The two hypothesized neural levels of WM during any moment of cognition comprise (a) "binding" together of many distributed attribute representations within each respective WM chunk, and (b) combinatorial play among three or four WM chunk-representations. Anatomical and functional evidence of cortical unity through its depth suggests that cortex may be viewed as essentially planar in its distribution of activations. Thus, a moment's WM is hypothesized here to reside in myriad activated cortical planar "patches," each subdivided into up to four amoeboid "subpatches." Two different lines of topological reasoning suggest orderly associations of such representations. (1) The four-color principle of map topology, and the related K(4) is planar theorem of graph theory, imply that if a small cortical area is dynamically subdivided into no more than four, discretely bounded planar subareas, then each such segment has ample free access to each of the others. (2) A hypothetical alternative to such associative adjacency of simultaneously active cortical representations of chunk-attributes is associative overlap, whereby, in dense cortical neuropil, activated subpatches behave like Venn diagrams of intersecting sets. As the number of Venn-like coactive subpatches within a patch increases, maintaining ad hoc associativity among all combinations requires exponentially proliferating intersections. Beyond four, serpentine subpatch shapes are required, which could easily lead to pathologies of omission or commission. As hypothesized by many researchers, the binding of the widely distributed cortical modules that represent a given chunk may involve synchrony or coherence of a single EEG frequency. Elsewhere, I have conjectured that such a binding frequency for a single chunk may bear a harmonic relationship with the additional EEG frequencies that are simultaneously binding the other WM chunks. Other possible mechanisms of binding have also been hypothesized. Whatever the mechanism, the many attributes of a moment's complement of three or four WM chunks must generally have an accidental relationship with the spatial distribution of the cortical feature analyzers that must be activated to represent those attributes. Therefore, the cortex may need, and have, comprehensive anatomical connections of each of its modules for representing an attribute (or of small redundant module groupings) with every other. If such whole-part cortico-cortical connections are somehow exploited not only to fully represent each cognitive chunk in its bound-together attributes, but also to bring the major business of intensive WM information processing down to the level of local circuits, in the sorts of topological patterning hypothesized here, there may be two adaptive results: (1) Time and other economies would be achieved in the reduction of activity in distant cortico-cortical connections to lower-energy global orchestration, or binding processes. (2) The piecemeal local topological limit to four subpatches would be writ large, across the entire cortex, preventing an unconstrained combinatorial explosion of associations among all attributes of all three or four simultaneously active chunks. Such hypothetical convergence to foci in local subpatch interactions might take place primarily in association cortex, and/or it might involve temporary shifts in response properties in some cortical subpat might involve temporary shifts in response properties in some cortical subpatches. Quantitative studies of the densely packed cortical fine structure, by Braitenberg and Schüz, and others, seem potentially consistent with this vision of cortical function in cognition.

A "theory of relativity" for cognitive elasticity of time and modality dimensions supporting constant working memory capacity: involvement of harmonics among ultradian clocks?

1. The capacity of working memory (WM) for about 7+/-2 ("the magical number") serially organized simple verbal items may represent a fundamental constant of cognition. Indeed, there is the same capacity for sense of familiarity of a number of recently encountered places, observed in radial maze performance both of lab rats and of humans. 2. Moreover, both species show a peculiar capacity for retaining WM of place over delays. The literature also describes paradoxes of extended time duration in certain human verbal recall tasks. Certain bird species have comparable capacity for delayed recall of about 4 to 8 food caches in a laboratory room. 3. In addition to these paradoxes of the time dimension with WM (still sometimes called "short-term" memory) there are another set of paradoxes of dimensionality for human judgment of magnitudes, noted by Miller in his classic 1956 paper on "the magical number." We are able to reliably refer magnitudes to a rating scale of up to about seven divisions. Remarkably, that finding is largely independent of perceptual modality or even of the extent of a linear interval selected within any given modality. 4. These paradoxes suggest that "the magical number 7+/2" depends on fundamental properties of mammalian brains. 5. This paper theorizes that WM numerosity is conserved as a fundamental constant, by means of elasticity of cognitive dimensionality, including the temporal pace of arrival of significant items of cognitive information. 6. A conjectural neural code for WM item-capacity is proposed here, which extends the hypothetical principle of binding-by-synchrony. The hypothesis is that several coactive frequencies of brain electrical rhythms each mark a WM item. 7. If, indeed, WM does involve a brain wave frequency code (perhaps within the gamma frequency range that has often been suggested with the binding hypothesis) mathematical considerations suggest additional relevance of harmonic relationships. That is, if copresent sinusoids bear harmony-like ratios and are confined within a single octave, then they have fast temporal properties, while avoiding spurious difference rhythms. Therefore, if the present hypothesis is valid, it implies a natural limit on parallel processing of separate items in organismic brains. 8. Similar logic of periodic signals may hold for slower ultradian rhythms, including hypothetical ones that contribute to time-tagging and fresh sense of familiarity of a day's event memories. Similar logic may also hold for spatial periodic functions across brain tissue that, hypothetically, represent cognitive information. Thus, harmonic transitions among temporal and spatial periodic functions are a possible vehicle for the cognitive dimensional elasticity that conserves WM capacity. 9. Supporting roles are proposed of (a) basal ganglia, as a high-capacity cache for traces of recent experience temporarily suspended from active task-relevant processing and (b) of hippocampus as a phase and interval comparator for oscillating signals, whose spatiotemporal dynamics are topologically equivalent to a toroidal grid.