The nested hierarchy of overt, mouthed, and imagined speech activity evident in intracranial recordings

Recent studies have demonstrated that it is possible to decode and synthesize various aspects of acoustic speech directly from intracranial measurements of electrophysiological brain activity. In order to continue progressing toward the development of a practical speech neuroprosthesis for the individuals with speech impairments, better understanding and modeling of imagined speech processes are required. The present study uses intracranial brain recordings from participants that performed a speaking task with trials consisting of overt, mouthed, and imagined speech modes, representing various degrees of decreasing behavioral output. Speech activity detection models are constructed using spatial, spectral, and temporal brain activity features, and the features and model performances are characterized and compared across the three degrees of behavioral output. The results indicate the existence of a hierarchy in which the relevant channels for the lower behavioral output modes form nested subsets of the relevant channels from the higher behavioral output modes. This provides important insights for the elusive goal of developing more effective imagined speech decoding models with respect to the better-established overt speech decoding counterparts.

Investigating the Link Between Linguistic and Non-Linguistic Cognitive Control in Bilinguals Using Laplacian-Transformed Event Related Potentials

Bilinguals' need to suppress the activation of their other language while speaking has been proposed to result in enhanced cognitive control abilities outside of language. Several studies therefore suggest shared cognitive control processes across linguistic and non-linguistic tasks. Here we investigate this potential overlap using scalp electroencephalographic recordings and the Laplacian transformation, providing an estimation of the current source density and enabling the separation of EEG components in space. Fourteen Spanish-English bilinguals performed a picture-word matching task contrasting incongruent trials using cross-linguistic false cognates (e.g., a picture - foot, overlaid with distractor text: the English word PIE, i.e., the false cognate for the Spanish pie meaning "foot") with congruent trials (matching English picture names and words, i.e., a picture - foot, with overlaid text: the English word FOOT), and an unrelated control condition. In addition, participants performed an arrow-version of the Eriksen flanker task. Worse behavioral performance was observed in incongruent compared to congruent trials in both tasks. In the non-linguistic task, we replicated the previously observed congruency effect on a medial-frontal event-related potential (ERP) peaking around 50 ms before electromyography (EMG) onset. A similar ERP was present in the linguistic task, was sensitive to congruency, and peaked earlier, around 150 ms before EMG onset. In addition, another component was found in the linguistic task at a left lateralized anterior frontal site peaking around 200 ms before EMG onset, but was absent in the non-linguistic task. Our results suggest a partial overlap between linguistic and non-linguistic cognitive control processes and that linguistic conflict resolution may engage additional left anterior frontal control processes.

Characterizing multi-word speech production using event-related potentials

Event-related potentials (ERPs) derived from electroencephalography (EEG) have proven useful for understanding linguistic processes during language perception and production. Words are commonly produced in sequences, yet most ERP studies have used single-word experimental designs. Single-word designs reduce potential ERP overlap in word sequence production. However, word sequence production engages brain mechanisms in different ways than single word production. In particular, speech monitoring and planning mechanisms are more engaged than for single words since several words must be produced in a short period of time. This study evaluates the feasibility of recording ERP components in the context of word sequence production, and whether separate components could be isolated for each word. Scalp EEG data were acquired, while participants recited word sequences from memory at a regular pace, using a tongue-twister paradigm. The results revealed fronto-central error-related negativity, previously associated with speech monitoring, which could be distinguished for each word. Its peak amplitude was sensitive to Cycle and Phonological Similarity. However, an effect of sequential production was also observable on baseline measures, indicating baseline shifts throughout the word sequence due to concurrent sustained medial-frontal EEG activity. We also report a late left anterior negativity (LLAN), associated with verbal response planning and execution, onsetting around 100 ms before the first word in each cycle and sustained throughout the rest of the cycle. This work underlines the importance of considering the contribution of transient and sustained EEG activity on ERPs, and provides evidence that ERPs can be used to study sequential word production.

Neural Underpinnings of Proactive Interference in Working Memory: Evidence From Patients With Unilateral Lesions

Proactive interference in working memory refers to the fact that memory of past experiences can interfere with the ability to hold new information in working memory. The left inferior frontal gyrus (LIFG) has been proposed to play an important role in resolving proactive interference in working memory. However, the role of white matter pathways and other cortical regions has been less investigated. Here we investigated proactive interference in working memory using the Recent Probes Test (RPT) in 15 stroke patients with unilateral chronic lesions in left (n = 7) or right (n = 2) prefrontal cortex (PFC), or left temporal cortex (n = 6). We examined the impact of lesions in both gray and white matter regions on the size of the proactive interference effect. We found that patients with left PFC lesions performed worse overall, but the proactive interference effect in this patient group was comparable to that of patients with right PFC lesions, temporal lobe lesions, and controls. Interestingly, the size of the interference effect was significantly correlated with the degree of damage in the extreme/external capsule and marginally correlated with the degree of damage in the inferior frontal occipital fasciculus (IFOF). These findings suggests that ventral white matter pathways connecting the LIFG to left posterior regions play a role in resolving proactive interference in working memory. This effect was particularly evident in one patient with a very large interference effect (>3 SDs above controls) who had mostly spared LIFG, but virtually absent ventral white matter pathways (i.e., passing through the extreme/external capsules and IFOF). This case study further supports the idea that the role of the LIFG in resolving interference in working memory is dependent on connectivity with posterior regions via ventral white matter pathways.

Roles of ventral versus dorsal pathways in language production: An awake language mapping study

Human language is organized along two main processing streams connecting posterior temporal cortex and inferior frontal cortex in the left hemisphere, travelling dorsal and ventral to the Sylvian fissure. Some views propose a dorsal motor versus ventral semantic division. Others propose division by combinatorial mechanism, with the dorsal stream responsible for combining elements into a sequence and the ventral stream for forming semantic dependencies independent of sequential order. We acquired data from direct cortical stimulation in the left hemisphere in 17 neurosurgical patients and subcortical resection in a subset of 10 patients as part of awake language mapping. Two language tasks were employed: a sentence generation (SG) task tested the ability to form sequential and semantic dependencies, and a picture-word interference (PWI) task manipulated semantic interference. Results show increased error rates in the SG versus PWI task during subcortical testing in the dorsal stream territory, and high error rates in both tasks in the ventral stream territory. Connectivity maps derived from diffusion imaging and seeded in the tumor sites show that patients with more errors in the SG than in the PWI task had tumor locations associated with a dorsal stream connectivity pattern. Patients with the opposite pattern of results had tumor locations associated with a more ventral stream connectivity pattern. These findings provide initial evidence using fiber tract disruption with electrical stimulation that the dorsal pathways are critical for organizing words in a sequence necessary for sentence generation, and the ventral pathways are critical for processing semantic dependencies.

Double dissociation of the roles of the left and right prefrontal cortices in anticipatory regulation of action

Recent actions can benefit or disrupt our current actions and the prefrontal cortex (PFC) is thought to play a major role in the regulation of these actions before they occur. The left PFC has been associated with overcoming interference from past events in the context of language production and working memory. The right PFC, and especially the right IFG, has been associated with preparatory inhibition processes. But damage to the right PFC has also been associated with impairment in sustaining actions in motor intentional disorders. Moreover, bilateral dorsolateral PFC has been associated with the ability to maintain task-sets, and improve the performance of current actions based on previous experience. However, potential hemispheric asymmetries in anticipatory regulation of action have not yet been delineated. In the present study, patients with left (n=7) vs. right (n=6) PFC damage due to stroke and 14 aged- and education-matched controls performed a picture naming and a verbal Simon task (participants had to say "right" or "left" depending on the color of the picture while ignoring its position). In both tasks, performance depended on the nature of the preceding trial, but in different ways. In the naming task, performance decreased if previous pictures were from the same rather than from different semantic categories (i.e., semantic interference effect). In the Simon task, performance was better for both compatible (i.e., response matching the position of the stimulus) and incompatible trials when preceded by a trial of the same compatibility (i.e. Gratton effect) relative to sequential trials of different compatibility. Left PFC patients were selectively impaired in picture naming; they had an increased semantic interference effect compared to both right PFC patients and aged-matched controls. Conversely, right PFC patients were selectively impaired in the Simon task compared to controls or left PFC patients; they showed no benefit when sequential trials were compatible (cC vs. iC trials) or a decreased Gratton effect. These results provide evidence for a double dissociation between left and right PFC in the anticipatory regulation of action. Our results are in agreement with a preponderant role of the left PFC in overcoming proactive interference from competing memory representations and provide evidence that the right PFC, plays a role in sustaining goal-directed actions consistent with clinical data in right PFC patients with motor intentional disorders.

Protein content of seed: increase improves growth and yield

Oat seeds with a higher protein content as a result of chemical applications in 1967 yielded 21 to 42 percent more grain in 1968. Wheat seed, whether from Michigan, Illinois, or Mexico, that contained more protein as a result of field applications of chemicals or nitrogen developed into larger seedlings. The content of protein in the seed correlated with subsequent growth and yield, indicating that the amount of endogenous protein or of a proteinaceous moiety, which can be controlled, may be an important factor in subsequent yield of major agronomic crops.

Rapid elicitation of second messengers by nanomolar doses of triacontanol and octacosanol

Triacontanol (TRIA) increases the dry weight and alters the metabolism of rice (Oryza sativa L.) seedlings within 10 min of application to either the shoots or roots. This activity is prevented if octacosanol (OCTA, C28 primary alcohol) is applied with the TRIA on the roots or shoots. Triacontanol activity is also stopped if the OCTA is applied at least 1 min before the TRIA on the opposite part of the seedling.Triacontanol rapidly elicits a second messenger that moves rapidly throughout the plant resulting in stimulation of growth (dry-weight increase) and water uptake. Octacosanol also produces a second messenger that inhibits TRIA activity. We have named the putative secondary messengers elicited by TRIA and OCTA, TRIM and OCTAM, respectively. The water-soluble TRIM extracted from plants treated with TRIA increases the growth of rice seedlings about 50% more than extracts from untreated plants, within 24 h of application. Both OCTAM and OCTA inhibit the activity of TRIA but not of TRIM.The TRIA messenger was isolated from rice roots within 1 min of a foliar application of TRIA. The TRIM elicited by TRIA will pass through a 4-mm column of water connecting cut rice shoots with their roots and can also be recovered from water in which cut stems of TRIA-treated plants have been immersed. Triacontanol applied to oat (Avena sativa L.) or tomato (Lycopersicon esculentum Mill.) shoots connected to rice roots by a 4-mm water column also results in the appearance of TRIM in rice roots.

Effect of Triacontanol on Chlamydomonas: II. Specific Activity of Ribulose-Bisphosphate Carboxylase/Oxygenase, Ribulose-Bisphosphate Concentration, and Characteristics of Photorespiration

Increased photosynthetic CO(2) assimilation by Chlamydomonas reinhardtii cells treated with triacontanol (TRIA) was not due to changes in glycolate excretion, CO(2) compensation point, or the sensitivity of photosynthetic CO(2) assimilation to O(2). Kinetic analysis of TRIA-treated cells showed that the increase in photosynthetic CO(2) assimilation was a result of an increase in the apparent V(max) for intact cells. The total activity of ribulose-P(2) carboxylase/oxygenase was higher in cell lysates from TRIA-treated cells. However quantification of this enzyme concentration by binding of [(14)C]carboxyarabinitol-P(2) did not show an increase in TRIA-treated cells. Thus, there was an increase in the specific activity of ribulose-P(2) carboxylase/oxygenase extracted from Chlamydomonas cells treated with TRIA. TRIA alone had no effect on the activity of the enzyme in cell lysates from Chlamydomonas or purified from spinach (Spinacia oleracea L.) leaves.The ribulose-P(2) pool was 50 to 60% higher in cells treated with TRIA that were assayed for photosynthetic CO(2) assimilation at high- and low-CO(2). TRIA also increased ribulose-P(2) levels in the absence of CO(2) in the light with atmospheres of N(2) or N(2) with 21% O(2).

Effect of Triacontanol on Chlamydomonas: I. Stimulation of Growth and Photosynthetic CO(2) Assimilation

Treatment of Chlamydomonas reinhardtii cells, cultured at 5% CO(2), with 1 to 1000 micrograms triacontanol (TRIA) per liter resulted in 21 to 35% increases in cell density, 7 to 31% increases in total chlorophyll, and 20 to 100% increases in photosynthetic CO(2) assimilation. The increase in CO(2) fixation with TRIA treatment occurred before, and was independent of, increases in total chlorophyll or cell number. Chlamydomonas cells responded to a broad range of TRIA concentrations that were at least one order of magnitude above the optimum concentration established for higher plants. The necessity for larger concentrations of TRIA may be due to destabilizing effects of Ca(2+) and K(+) present in the Chlamydomonas growth medium. These ions caused flocculation of the colloidally dispersed TRIA in apparent competition with binding of [(14)C]TRIA to Chlamydomonas cells. Octacosanol inhibited the effect of TRIA on photosynthetic CO(2) assimilation. TRIA treatment did not alter the distribution of (14)C-label among photosynthetic products. The effect of TRIA on photosynthetic CO(2) assimilation increased with time after treatment up to 3 days. Chlamydomonas cells that had been grown at low-CO(2) (air) did not respond to TRIA, and transfer of high-CO(2) (5%) grown cells that had responded to TRIA to a low-CO(2) atmosphere resulted in a loss of the effect of TRIA. The effect of pH on photosynthetic CO(2) assimilation indicated that CO(2) is probably the species of inorganic carbon utilized by control and TRIA-treated Chlamydomonas cells.

Growth Enhancement of Plants by Femtomole Doses of Colloidally Dispersed Triacontanol

Colloidal dispersions of crystalline 1-triacontanol in water, upon foliar application to corn (Zea mays L.) seedlings, resulted in growth increases at femtomole dosages (spray concentrations as low as 1 nanogram per cubic decimeter). The maximum growth increase occurred at 100 nanograms per cubic decimeter; at both higher and lower concentrations lessened growth increase was observed. The dispersions were prepared by sonication, with control of temperature and composition. Selected surfactants, which facilitate the dispersion process, are effective at 1 percent of the 1-triacontanol composition and are nontoxic.

Rapid Growth and Apparent Total Nitrogen Increases in Rice and Corn Plants following Applications of Triacontanol

Triacontanol (TRIA) increased fresh and dry weight and total reducible nitrogen (total N) of rice (Oryza sativa L.) seedlings within 40 minutes. Increases in total N in the supernatants from homogenates of corn (Zea mays L.) and rice leaves treated with TRIA for one minute before grinding occurred within 30 and 80 minutes, respectively. The source for the increase was investigated utilizing atmospheric substitution and enrichment and depletion studies with (15)N. The increase in total N in seedlings was shown to be independent of method of N analysis and the presence of nitrate in the plants. Automated Kjeldahl determinations showing apparent increases in N composition due to TRIA were shown to be correlated with hand Kjeldahl, elemental analysis, and chemiluminescent analysis in three independent laboratories. TRIA did not alter the nitrate uptake or endogenous levels of nitrate in corn and rice seedlings. Enrichment experiments revealed that the total N increases in rice seedlings, in vivo, and in supernatants of corn leaf homogenates, in vitro, are not due to atmospheric N(2). TRIA increased the soluble N pools of the plants, specifically the free amino acid and soluble protein fractions. No differences in depletion or enrichment of (15)N incorporated into soluble and insoluble N fractions of rice seedlings could be detected on an atom per cent (15)N basis. The apparent short-term total N increases cannot be explained by current knowledge of major N assimilation pathways. TRIA may stimulate a change in the chemical composition of the seedlings, resulting in interference with standard methods of N analysis.

Environmental Parameters Affecting Dark Response of Rice Seedlings (Oryza sativa L.) to Triacontanol

Triacontanol applied to IR-8 rice (Oryza sativa L.) seedlings in nutrient solution caused an increase in dry weight during a 6-hour dark period. This increase was altered by atmospheric CO(2) and O(2) concentrations. The largest growth response occurred from 200 to 350 muliters/liter CO(2) with 5% O(2). The treated seedlings did not fix atmospheric CO(2) in the dark, and the immediate products of photosynthesis were not involved in the dry weight increase. The growth response was characterized by an increase in soluble and insoluble Kjeldahl-N, and soluble carbohydrates. The response curve for dry weight increase was a linear function of log presentation time of triacontanol. The response exhibited an apparent K(dose) of 25 minutes in 10 mug/liter triacontanol in the dark and 18 minutes in the light. Concentrations of 50 mug/liter and higher inhibited growth.

Effect of triacontanol on plant cell cultures in vitro

Triacontanol [CH(3)(CH(2))(28)CH(2)OH] increased growth in vitro of cell cultures of haploid tobacco (Nicotiana tabacum). The fresh weight of cell cultures of tomato (Lycopersicon esculentum), potato (Solanum tuberosum), bean (Phaseolus vulgaris), and barley (Hordeum vulgare x H. jubatum) was also increased. The increase in growth of tobacco callus seems to have been due to an increase in cell number. Another long chain alcohol, octocosanol [CH(3)(CH(2))(26)CH(2)OH], did not increase the growth of tobacco cell cultures.

Triacontanol: A New Naturally Occurring Plant Growth Regulator

Alfalfa meal and chloroform extracts of the meal have increased the growth and yield of several plant species. A crystalline substance isolated from the active fraction of alfalfa meal increased the dry weight and water uptake of rice seedlings when sprayed on the foliage or applied in nutrient culture. The substance was identified as triacontanol by mass spectrometry. Sprays containing this compound also increased the growth of corn, and barley grown in soil. Authentic triacontanol produced a similar response over a wide range of concentrations on rice grown in nutrient cultures and tomatoes grown in soil.

Superoxide dismutases: I. Occurrence in higher plants

Shoots, roots, and seeds of corn (Zea mays L., cv. Michigan 500), oats (Avena sativa L., cv. Au Sable), and peas (Pisum sativum L., cv. Wando) were analyzed for their superoxide dismutase content using a photochemical assay system consisting of methionine, riboflavin, and p-nitro blue tetrazolium. The enzyme is present in the shoots, roots, and seeds of the three species. On a dry weight basis, shoots contain more enzyme than roots. In seeds, the enzyme is present in both the embryo and the storage tissue. Electrophoresis indicated a total of 10 distinct forms of the enzyme. Corn contained seven of these forms and oats three. Peas contained one of the corn and two of the oat enzymes. Nine of the enzyme activities were eliminated with cyanide treatment suggesting that they may be cupro-zinc enzymes, whereas one was cyanide-resistant and may be a manganese enzyme. Some of the leaf superoxide dismutases were found primarily in mitochondria or chloroplasts. Peroxidases at high concentrations interfere with the assay. In test tube assays of crude extracts from seedlings, the interference was negligible. On gels, however, peroxidases may account for two of the 10 superoxide dismutase forms.

Superoxide Dismutases: II. Purification and Quantitative Relationship with Water-soluble Protein in Seedlings

Superoxide dismutase was purified from pea (Pisum sativum L., cv. Wando) seeds and corn (Zea mays L., cv. Michigan 500) seedlings. The purified pea enzyme eluting as a single peak from gel exclusion chromatography columns contained the three electrophoretically distinct bands of superoxide dismutase characterizing the crude extract. The purified corn enzyme eluted as the same peak as the pea enzyme, and contained five of the seven active bands found in the crude extract. The similar molecular weights and the cyanide sensitivities of these bands indicated that they are probably isozymes of a cupro-zinc superoxide dismutase. One of the remaining corn bands was shown to be a peroxidase.Superoxide dismutase accounted for 1.6 to 2.4% of the water-soluble protein in seedlings of corn, peas, and oats (Avena sativa L., cv. Au Sable). The superoxide dismutase activity per plant and per milligram water-soluble protein considerably increased during germination of oats and during greening and hook opening of peas.

Superoxide dismutases: I. Occurrence in higher plants

Shoots, roots, and seeds of corn (Zea mays L., cv. Michigan 500), oats (Avena sativa L., cv. Au Sable), and peas (Pisum sativum L., cv. Wando) were analyzed for their superoxide dismutase content using a photochemical assay system consisting of methionine, riboflavin, and p-nitro blue tetrazolium. The enzyme is present in the shoots, roots, and seeds of the three species. On a dry weight basis, shoots contain more enzyme than roots. In seeds, the enzyme is present in both the embryo and the storage tissue. Electrophoresis indicated a total of 10 distinct forms of the enzyme. Corn contained seven of these forms and oats three. Peas contained one of the corn and two of the oat enzymes. Nine of the enzyme activities were eliminated with cyanide treatment suggesting that they may be cupro-zinc enzymes, whereas one was cyanide-resistant and may be a manganese enzyme. Some of the leaf superoxide dismutases were found primarily in mitochondria or chloroplasts. Peroxidases at high concentrations interfere with the assay. In test tube assays of crude extracts from seedlings, the interference was negligible. On gels, however, peroxidases may account for two of the 10 superoxide dismutase forms.

Growth responses of rice seedlings to triacontanol in light and dark

Triacontanol, a 30-carbon primary alcohol, applied in nutrient culture solutions to rice (Oryza sativa L.) seedlings at 2.3×10(-8) M (10 μg/l), caused an increase in dry weight and leaf area of the whole plants. The response could be observed as early as 3 h of treatment. It was observed at relatively high and low light intensities as well as in the dark where control plants lost but triacontanol-treated plants gained in dry weight. The dry weight gain in the dark was, however, eliminated by removing CO2 from the atmosphere. Triacontanol-treated plants also increased their content of Kjeldahl-N and contained 30% more total N per plant than controls after 6 h in the dark.

Endosperm protein of wheat seed as a determinant of seedling growth

Seed of a Mexican semidwarf wheat (Triticum aestivum L. cv. Inia 66), was obtained from a nitrogen fertilizer field trial grown in Mexico. A high positive correlation was obtained between seed protein content and seedling dry weight after 3 weeks growth (r = +0.92(**)). The seedling dry weight was positively related to the protein content of the aleurone layer and endosperm, but not to the embryo. Small, 35 milligrams, high protein seeds (4.7 milligrams protein per seed) produced larger seedlings than large, 45 milligrams, low protein seeds (4.3 milligram protein per seed). There was no difference in the weight or protein content of embryos from low and high protein seeds and their growth was similar. Composite seeds of the two protein levels were produced by transferring embryos from one endosperm type to the other. After 4 weeks, there was no difference between the different embryo types grown on the same endosperm type. High protein endosperm produced more vigorous seedlings regardless of the embryo type grown on it, indicating that the factor(s) responsible for the greater growth of high protein seed is in the endosperm.

The increase in nitrate reductase activity and protein content of plants treated with simazine

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Effect of simazine on nitrate reductase activity in corn

The nutritional and environmental parameters required for eliciting increases in the nitrogen content and growth of corn (Zea mays L.) by non-toxic levels of simazine have been established. Corn seedlings with the endosperm removed 10 days after germination, proved to be a suitable test species. The addition of simazine to the root-zone area of corn plants grown under both sub-optimal temperatures and low nitrate levels, increased the nitrogen content and dry weight of the plants by 20 to 25%. This increase was found to be associated with an effect on nitrate reductase.

Amitrole Translocation in Agropyron repens Increased by the Addition of Ammonium Thiocyanate

The mechanism for the enhancement of amitrole activity on quackgrass (Agropyron repens) by the addition of ammonium thiocyanate was studied. Absorption and translocation of C(14)-amitrole after applications to foliage were determined by a direct count of the radioactivity in the wash solution and plant extracts. Regardless of the time of application, the addition of ammonium thiocyanate did not alter the amount of C(14)-amitrole absorbed. Ammonium thiocyanate (5000 parts per million) greatly increased the amount of carbon-14 translocated. This increase may account for the greater herbicidal effectiveness of the mixture of amitrole and ammonium thiocyanate.