Rhythmic Sequences Research Articles

Fast activity and oscillatory potential of carp retina in the frequency domain

There are two kinds of fast activity in the ERG: fast retinal potentials (FRP), an irregular series of spiky wavelets and oscillatory potentials (OP), a rhythmic sequence of events. Corneal ERG from nine intact young carps, evoked by extended pulses of diffuse white light under mesopic adaptation, displayed two different groups of wavelets related to ON and OFF, respectively. Stimulation and recording conditions were established to permit separate Fourier analysis of both groups of wavelets. Power distributions of normalized ON spectra showed both a wide dispersion and a high inter-subject variability. All normalized OFF spectra showed, instead, components within a narrow band from 52 to 56 Hz, most of them maximum relative power peaks. It is concluded that FRP originating in highly labile sources dominate ON fast activity, while the predominant OFF fast activity are OP originating in a stable discrete source.

The Role of Melodic and Verbal Organization in the Reproduction of Rhythmic Groups by Children

Children of 5 to 6 years are generally thought not to have acquired a sense of stable key in music. This experiment shows that specialized tutoring allows them to acquire and use the specific functions of the tonic and dominant as points of stability and boundaries for grouping rhythmic sequences in a reproduction task. Untrained children of the same age do not use the cues provided by the tonal system, but lean rather upon verbal boundaries (in the sense of syntactic constituents). Three analyses of the results demonstrated that (a) verbal and melodic cues superimposed onto rhythmic models were used differently according to the musical competence of the child; (b) children do not always respect tempo or accentuation, but generally produce highly structured sequence; (c) the temporal sequences reproduced have a hierarchical organization on two levels: local organization, which can be considered related to episodic memory and global organization, which is related to semantic memory and so is dependent on the subject's musical knowledge.

The recommended Cambrian–Ordovician global Boundary stratotype of the Xiaoyangqiao section (Dayangcha, Jilin Province), China

AbstractThis paper provides a brief outline of the current, detailed inter-disciplinary work on the Xiaoyangquiao section, trying to expose all the aspects for reference tied to the Global Single Stratigraphic Point (GSSP) Concept for defining the Cambrian–Ordovician Boundary. The 45 m critical interval of this section outcrops very well along the steep bank of a stream and is free from folding, faulting, intrusions, and has not been affected by weathering. Colour alternation of conodonts and acritarchs, and crystallinity indices of illite all indicate a maximum thermal grade of 100 °C. The lithofacies, being of great lateral persistence for a hundred kilometres, consists mainly of a rhythmical sequence of lime mudstone and shales deposited in a moderately deep outer shelf environment of quiet water, well below the normal storm wave base. Chemical investigation of the rocks demonstrates strong positive correlation between A12O3content and those of K2O, MgO, Fe2O3, TiO2, Be, Cr, Co, Ni, Zn and Ba, indicating these components are tied to the clay fractions. A stable depositional environment is demonstrated by the uniform chemistries through the boundary interval. Close to the boundary itself P2O5contents are low, indicating continuous sedimentation at fairly substantial rates.The major biological events, the biostratigraphic framework, and the stratigraphic range of conodont, graptolite, trilobite, and acritarch taxa are illustrated briefly with diagrams. Following the majority views of the Calgary Plenary Session, the boundary level is to be chosen at a point marked by the First Appearance Datum (FAD) of the selected conodont taxon or taxa in the vicinity of the level close to, but below, the first influx of nematophorous graptolites. The following four points marked by the incoming of conodont taxon or taxa are recommended for consideration of the ‘Golden Spike'‘: (1) FAD ofCordylodus intermediusat 5.28 m below the first influx of nematophorous graptolites; (2) FAD ofHirsutodontus simpler–Cordylodus drucei–Albiconus postcostatusat 5.23 m; (3)FADofSemiacontiodus lavadamensis–Utahconus utahensis–Monocostodus sevierensisat 3.85 m; (4)FADofCordylodus lindstromiat 2.23 m. For the following reasons the FAD ofH. simplex–C. drucei–A. postcostatusis favoured: (1) the taxa are all distinct and widely dispersed; (2) intensive evolutionary change took place in conodonts, graptolites, trilobites and acritarchs prior to or after this point; all the fossil groups occur together, providing correlation with many regions throughout the world; (3) the point is in a position between the previously widely accepted boundary levels based on graptolites and trilobites; (4) the proposed point lies within a thin, laterally persistent, rhythmical sequence. The FAD ofCordylodus lindstromiis also a favourable point, sharing many advantages mentioned above. But this point is less satisfactory in being defined by the FAD of a single taxonC. lindstromiwhich also has an extremely small population size.An isochron age of 500.7 ± 7.4 Ma is determined from clay fractions of mudstones 8.5 m below the proposed point by means of the Rubidium–Strontium method.The ɛND signature determined from conodonts, trilobites hyolithids and acrotretid brachiopods has a mean value of −6.7, comparable with that of the coeval oceanic water mass occupying southeastern North America and Europe, and indicating that northeastern China bordered the same ocean. The mean Tdm model age determined was 1.26 Ga at the time of sedimentation, compatible with the mean Tdm model age of approximately 1.1 Ga for the Pacific Ocean today. The relatively low value of the Tdm model age indicates a substantial input from young orogenic volcanic island arcs and terranes.

Hemispheric Asymmetry in the Matching of Melodies to Rhythm Sequences Tapped in the Right and Left Palms

Two experiments were conducted to investigate the ability of the cerebral hemispheres to match rhythm sequences tapped in the palms of the hands to tape-recorded melodies. Reaction time (RT) for same/different judgments and accuracy of responses served as the dependent measures. In Experiment 1, for the RT data, a left palm/right hemisphere (LP/RH) advantage was found in the ability to match tapped rhythms to tape-recorded melodies, but only on Different trials. On Same trials (which were found to be somewhat easier), both hemispheres were equally efficient at making such comparisons. In Experiment 2, there was no reliable difference between the LP/RH and the RP/LH in the ability to match tapped rhythms to tape-recorded rhythm sequences which were devoid of melodic intonation (i.e., the sound of two blocks of wood struck together in a specified rhythm). The results of these experiments taken in composite lend support to the contention that the right hemisphere advantage typically reported for the processing of musical stimuli is primarily related to pitch and/or intonation rather than rhythm.

Studies Illuminate Hazards of Ingested Radiation

DIP... PAINT... LICK the brush. The rhythmic sequence was second nature to those known as luminators during the 1920s. Their task was simple—to apply radium paint to the tiny numerals encircling watch dials. Their occupational hazards were manifold—osteomyelitis, aplastic anemia, osteosarcoma, and mastoid carcinoma. Dial painting required a deft hand and a finely pointed brush. While the first attribute may have been hereditary, the second was easily acquired. All it took to keep a brush pointed was a quick touch to the lips or tongue. "Lip tipping" passed particles of the sticky paint to the teeth and tongue; it also transferred from 3 to 43 μg of radioactive substances each day. Thus, in a few years' time luminators could easily have swallowed 5 mg or more, at least 1 mg of which would be deposited in their bones, spleen, and liver, where it would remain, emitting a steady stream of

Cortically induced masticatory rhythm in masseter motoneurons after blocking inhibition by strychnine and tetanus toxin

In the first series of experiments, we studied whether or not strychnine (STR)-resistant inhibition of masseter motoneurons (MASS·MNs) was involved in their rhythmical inhibition that occurs during masticatory activity, induced by repetitive stimulation of the cortical masticatory area (CMA) in the cat. After systemic STR injection, repetitive CMA stimulation induced rhythmically alternating activity in the masseteric and anterior digastric nerves with a shorter cycle time than before STR-administration. The short-latency IPSPs in the MASS·MNs evoked by single shocks applied to the CMA were abolished. In contrast, repetitive CMA stimulation still induced a rhythmical alternation of EPSPs and IPSPs in the MASS·MNs, although the IPSPs were significantly reduced in amplitude. In the second series, we attempted to abolish the STR-resistant component of the rhythmical IPSP with tetanus toxin (TT). This was injected into one superficial masseter muscle of the guinea pig. In the majority of animals repetitive CMA stimulation induced a tonic EMG superimposed by rhythmical bursts in the TT-intoxicated masseter muscle. Repetitive CMA stimulation induced a rhythmical sequence of EPSPs and superimposed spikes in the MASS·MNs innervating the TT-intoxicated masseter muscle in paralyzed guinea pigs. It was concluded that: (1) the cortically-evoked short-latency inhibition of MASS·MNs is STR-sensitive, as is part of the rhythmical inhibition during CMA-induced mastication; and (2) rhythmical inhibition is not essential for the central generation of the rhythmical activity in the MASS·MNs.

Cortically induced masticatory rhythm in masseter motoneurons after blocking inhibition by strychnine and tetanus toxin.

In the first series of experiments, we studied whether or not strychnine (STR)-resistant inhibition of masseter motoneurons (MASS . MNS) was involved in their rhythmical inhibition that occurs during masticatory activity, induced by repetitive stimulation of the cortical masticatory area (CMA) in the cat. After systemic STR injection, repetitive CMA stimulation induced rhythmically alternating activity in the masseteric and anterior digastric nerves with a shorter cycle time than before STR-administration. The short-latency IPSPS in the MASS . MNS evoked by single shocks applied to the CMA were abolished. In contrast, repetitive CMA stimulation still induced a rhythmical alternation of EPSPS and IPSPS in the MASS . MNS, although the IPSPS were significantly reduced in amplitude. In the second series, we attempted to abolish the STR-resistant component of the rhythmical IPSP with tetanus toxin (TT). This was injected into one superficial masseter muscle of the guinea pig. In the majority of animals, repetitive CMA stimulation induced a tonic EMG superimposed by rhythmical bursts in the TT-intoxicated masseter muscle. Repetitive CMA stimulation induced a rhythmical sequence of EPSPS and superimposed spikes in the MASS . MNS innervating the TT-intoxicated masseter muscle in paralyzed guinea pigs. It was concluded that: (1) the cortically-evoked short-latency inhibition of MASS . MNS is STR-sensitive, as is part of the rhythmical inhibition during CMA-induced mastication; and (2) rhythmical inhibition is not essential for the central generation of the rhythmical activity in the MASS . MNS.

Interregional model for deposition of Upper Cretaceous pelagic rhythmites, U.S. western interior

The Bridge Creek Member of the Greenhorn Limestone and Fort Hays Member of the Niobrara Chalk comprise rhythmic sequences of bioturbated pelagic limestone or chalk beds that alternate with generally shaly interbeds. Within each member individual couplets are time parallel and can be traced with great precision for hundreds of kilometers. Certain of the Bridge Creek beds can be traced from northeastern Kansas to the Four Corners area, a distance exceeding 1000 km. Regional stratigraphic analysis of these remarkable bedding sequences permits integration of concepts generated by several students of pelagic sedimentary sequences into a comprehensive model. In the basin center, Bridge Creek rhythms resulted from dilution cycles wherein a background of pelagic sedimentation was punctuated by episodes of increased siliciclastic influx and water column stratification. Consequent development of oxygen‐depleted bottom waters created high potential for preservation of laminae and organic matter in shaly interbeds. Within a given couplet, predominating influence of western siliciclastic source areas is evident in westward decrease of carbonate content in both bioturbated limestones and shaly interbeds, disappearance of one and then another of the limestone beds, and increase in abundance of the coarse detrital fraction. Toward the east, both bioturbated limestones and shaly interbeds grade progressively into chalky lithotypes. At some point where effects of detrital‐dilution episodes were minimal and the water was probably shallower, stratification of the water column was not possible, and interbeds are not only thinner but also bioturbated. Because of erosion this facies is not preserved in the Bridge Creek interval of Kansas, but it is exemplified there by the Fort Hays Member. Still farther eastward, where detrital influx was negligible, most of the Bridge Creek equivalent comprises a massive, bioturbated chalk sequence that lacks interbeds. This facies is preserved in northwestern Iowa. In condensed sections, the Bridge Creek Member contains considerable skeletal grainstone that bespeaks improved benthic circulation, even during deposition of shaly interbeds. The condensed sections developed on seafloor highs that apparently presaged the Laramide orogeny. The foregoing interpretation of regional variations in the Bridge Creek Member is generally applicable to the less widespread Fort Hays rhythmic sequence, in which simple dilution cycles seem to have predominated.

Pitch and rhythm paradoxes: comments on "Auditory paradox based on fractal waveform".

Schroeder [J. Acoust. Soc. Am. 79, 186-189 (1986)] describes the paradox of acoustic waveforms that sound lower when reproduced at higher speeds. The author has also demonstrated this paradox [J.C. Risset, J. Acoust. Soc. Am. 46, 88 (A) (1969); see also Seventh ICA, Budapest, S10, 613-616 (1971)]; in addition he has recently synthesized a rhythmic analog of the paradox, namely rhythmical sequences that can sound slower when reproduced at higher speeds.

Multielectrode analysis of coordinated, multisite, rhythmic bursting in cultured CNS monolayer networks

Laser-deinsulated, printed-circuit electrodes integrated into the floor of culture chambers have been used to monitor the spontaneous activity of mouse spinal monolayer cell cultures. This technique has allowed a multisite analysis of activity over long periods of time in closed chambers. In 63 cultures investigated 3-5 weeks after seeding, 89% included single- or multiunit bursting. Based on a subset of 40 cultures in which all electrodes were sequentially scanned, bursting was found on 41% of the active electrodes (approximately 38% of all units monitored). A total of 35% of the electrodes monitoring spontaneous bursting activity revealed rhythmic sequences that were usually coupled among multiple electrodes. Although most of this coupling was in-phase, three out of 40 cultures exhibited antiphasic bursting. In all cases where coupling was observed, each electrode monitored different burst compositions, demonstrating that the activity was generated by different units. Some rhythmic patterns persisted for over 12 hr and were observed in 400 mm2 monolayer cultures, as well as in much smaller 3 mm2 adhesion islands. The addition of 10 mM MgCl2 consistently blocked both random and patterned (i.e., bursting) spontaneous activity at all recording sites. Strychnine (10(-6) M) typically increased firing frequencies and either disrupted pretest bursting or generated rhythmic activity from random phasic patterns. In certain cases, strychnine also blocked activity on specific electrodes, indicating that glycine is not the only inhibitory transmitter involved. The spontaneous appearance of rhythmic activity in low-density, monolayer cell cultures established from dissociated and randomly seeded spinal tissue can be explained by one or a combination of two hypotheses: an inherent specificity of some interconnections in developing mammalian cultures and the generation of organized activity by random circuits at certain stages of complexity.

Disrupting the isochrony underlying rhythm: An asymmetry in discrimination

Recognition memory for equitone sequences was tested as a function of whether the pattern of stimulus onsets mapped easily onto an isochronous grid (rhythmic) or did not (disrupted). In a same-different task, discrimination between a rhythmic sequence and its disrupted variant was better when the rhythmic sequence was presented first and the disrupted variant second than vice versa. Analogous effects have been obtained for melodies and chord sequences as a function of tonal structure, and for text as a function of semantic and pragmatic coherence. In each domain, discrimination between coherent sequences and anomalous variants is better when the coherent version is presented first.

Processes controlling the heavy metal distribution in pacific ferromanganese nodules and crusts

The ferromanganese precipitates existing in deep-sea waters of the Pacific consist of two types of deposits: (1) nodules mainly are distributed in pelagic basins beneath the CCD (Calcite Compensation Depth) where the rate of sedimentation is low; (2) polymetallic encrustations are formed on exposed seamount rocks where currents prevent normal sediment accumulation. Nodules, being formed in areas bordering the equatorial zone of high biological productivity, grow by two different processes: (A) early diagenetic growth by supply of metals and metal compounds from pore water and (B) hydrogenetic growth by supply of colloidal particles from near-bottom seawater. These processes lead to different kinds of oxide and different metal contents. The diagenetic growth process takes place under oxidizing to suboxidizing conditions and is supplied by an ionic solution of Mn2+ and other divalent metal ions. The mobilization of Mn is caused by the decomposition of organic matter. The growth features of the early diagenetic nodules show alternating laminae of crystalline and amorphous material. These rhythmic sequences of different microlayers are explained by physico-chemical changes (variation of pH) in the microenvironment of the accreting nodule surface. The hydrogenetic crust growth on seamounts leads to ferromanganese precipitates which are in particular rich in Co. The Co concentration is inversely related to the water depth. Co is positively correlated to Mn which can be derived from the oxygen minimum zone. Contrary to the diagenetic nodule growth, the crust accretion is also a colloidal precipitation process. In the water column below the oxygen minimum zone, a mixture of particles of Mn-Fe-oxyhydroxide and silicate accrete together on the surface of substratum rocks. Surface chemical mechanisms control the enrichment of Ni, Co, Pb, and other metals from the seawater; for Pt, a coprecipitation with MnO2 caused by a redox reaction is proposed. Distinct oceanographical and geological conditions enable or promote, respectively, the ferromanganese crust formation on seamounts.

On marching to two different drummers: perceptual aspects of the difficulties.

People have remarkable difficulty generating two responses that must follow different temporal sequences, unless the temporal patterns are simply related (e.g., periods in 2:1, 3:1 relation). For example, it is hard to tap to two conflicting rhythms presented concurrently (i.e., a polyrhythm) using the right and left hands (Klapp, 1979), or to tap while articulating a conflicting speech utterance (Klapp, 1981). The present experiments indicate that difficulties in processing conflicting rhythms occur even when people must (a) merely monitor the stimuli and indicate the termination of one rhythmic sequence or (b) tap with a single hand. Responding to polyrhythms is thus difficult even without multiple limb coordination. Furthermore, the difficulty of two-handed tapping to polyrhythms that involve two different tones was found to decrease as the pitch difference between the tones was decreased. This result indicates that the difficulty of rhythmic coordination can be perceptually manipulated in a striking fashion. Polyrhythmic performance thus provides an excellent opportunity for examining possible interactions of perceptual and motor organizations.

Mathematical and statistical aids to evaluate data from renal patients

The monitoring of renal patients and the making of many decisions during their management involves consideration of sequences of numerical data. Renal function results after renal transplantation were used as an example of how graphical presentations, simple mathematical transforms, statistical evaluation and adjustments to the data, to take into account other biological and technical sources of error, can all contribute to better understanding. Experience with a statistical technique, the 4-state Kalman filter not often used in the biological sciences, was summarized and its use suggested as a method to quantitate some traditionally subjective decisions about individual patients, for example, the onset of allograft rejection. The method has identified in retrospect and in prospect events after transplantation earlier than did experienced clinicians. Other statistical techniques to set the sensitivity and specificity of monitoring methods, to detect change points and to quantitate rhythmic sequences of clinical data were discussed, with examples, and with increasing access to computers, these can be used more easily by nephrologists, transplant surgeons, and others.

Geochemical processes controlling the relationship between Co, Mn, and Fe in early diagenetic deep-sea nodules

Early diagenetic manganese nodules from the northeast Pacific nodule belt and from the southeast Pacific (Peru Basin) show primary growth features of dendritic microtextures consisting of alternating laminae of crystalline 10-Åmanganate (A1 substance) and amorphous material which is composed of an intimate mixture of ferric hydroxide, silicate, and δ-MnO 2 (A2 substance). The formation of rhythmic sequences of A1 and A2 microlayers is explained by physico-chemical changes in the peneliquid sediment layer and in the microenvironment of the accreting nodule surface: (a) upward diffusion of Mn 2+ in the interstitial water as a result of decay of organic matter and Mn mobilization; (b) oxidation of Mn 2+ and formation of 10-Åmanganate in the upper part of the peneliquid sediment layer, leading to pH depression in the microenvironment of the nodule surface which decreases the mobility of silicate, resulting in formation of A2 layers; (c) restoration of pH and renewed precipitation of 10-Åmanganate. Based on data of 171 bulk analyses and on electron microprobe investigations, interelement relationships between Co, Mn, and Fe are pointed out. Fe and Co show a significant positive correlation ( r = 0.84), while Mn and Co are poorly negatively correlated ( r = −0.21), assuming linear regression. The enrichment of Co within the amorphous A2 phase is attributed to specific surface adsorption and subsequent oxidation of Co 2+ to Co 3+ in the strong electric field of Si 4+. Robust complexes of Co(III) and ≡ FeH 2SiO 4 − prevent most of the Co from being available for the 10-Åmanganate precipitation. Concerning the relation between Mn and Fe and Co respectively, the highest correlation coefficients are obtained using an inverse logarithmic regression. Under early diagenetic conditions, the concentration and precipitation of Mn 2+ in the interstitial water depends on the redox gradient which is controlled by the amount of decomposing organic matter. The Nernst equation describes the relationship as a reciprocal logarithmic function. However, the quantities of colloidal ferric hydroxide and of dissolved silicate are not affected by variations of the redox potential. These different characteristics in the precipitation of Mn and the Fe- and Si-rich colloidal phase may cause the significantly negative logarithmic correlation of Mn versus Fe and Co, respectively.

The role of eclosion hormone in the larval ecdyses of Manduca sexta

Each larval moult in Manduca sexta consists of an identical series of developmental and behavioural events leading up to ecdysis. Injections of eclosion hormone into staged larvae in any instar resulted in the premature elicitation of the larval pre-ecdysis behaviour, comprising a rhythmic sequence of muscle contractions, followed by the larval ecdysis behaviour. A marked depletion of eclosion hormone stores form the ventral chain of ganglia coincided with each larval ecdysis and in the moult to the fifth instar, eclosion hormone activity appeared in the blood at the onset of the pre-ecdysis behaviour. Responsiveness to eclosion hormone for pre-ecdysis and ecdysis behaviour developed about 12 and 6 hr before normal ecdysis, respectively. Elicitation of ecdysis behaviour by exogenous hormone inhibited both subsequent behavioural responses to eclosion hormone and endogenous hormonal release. In conclusion, the behavioural programme involved in each larval ecdysis appears to be controlled by the eclosion hormone.

Bahama carbonate platforms — The deep and the past

Carbonate deposition prevailed for 150 Ma in the Bahama—Florida segment of the West Atlantic margin and provides an interesting test for actualism. Present-day facies patterns on the banks are controlled by the backward decrease of waves and tides and the concomitant increase of temperature and salinity variation. In the troughs, influx of sand and rubble from gravity flows varies with topography and distance from shallow-water sources and allows one to define facies belts: a rhythmic sequence of ooze and graded beds on the basin floors, subdivided into a basin-margin belt of coarse, thick turbidites and basin interior with fine turbidites; slope facies change with increase in height and declivity from accretionary to by-pass to erosional regimes. Stratigraphic history of the Bahamas is not simply a projection of the “Holo-Scene” back in time. Both long-term natural evolution (decrease in subsidence, upbuilding of the banks, submarine erosion) and outside factors (climate, eustacy) have caused significant changes. Since the Jurassic, the Bahamas seem to have evolved from a clastics-evaporite province to a single carbonate-evaporite platform and finally to an array of platforms and troughs. During the platform-trough stage, the rate of upbuilding of the platforms decreased, submarine canyon erosion increased. Platform flanks steepened as they grew higher and changed from accretionary to by-pass to erosional slopes. A change imposed by extraneous factors occurred in the Pliocene, when the Great Bahama Bank changed from a giant reef-rimmed atoll to a flat platform covered by oolites and peloid sands. The Bahamas share both long-term trends as well as random changes by extraneous factors with other platforms in the geologic record. Compared to ancient platforms, however, they are unusually long-lived and at a more advanced stage of growth, they are deeply dissected by erosion, their flanks are unusually high and steep and the troughs very narrow. The Neogene platform sequence is strongly controlled by eustatic sea-level fluctuations.

Glacial sediments from Weuda, Sri Lanka

Evidence for probable Paleozoic glaciation is reported for the first time from Sri Lanka. Rhythmic sequences containing clay/peat, sand, gravel and pebble layers occur in valleys underlain by Precambrian metamorphic rocks. Varve-like sediments and discshaped striated pentagonal pebbles characterize these sequences. This interpretation is also supported by granulometric data.

Facilitation and inhibition of jaw reflexes evoked by electrical stimulation of the cat's cerebral cortex.

The effects of electrical stimulation of the cerebral cortex on the monosynaptic jaw closing and the disynaptic jaw opening reflexes were studied in cats anaesthetized with chloralose. The time course of the reflex effects was recorded. Similar rhythmic sequences of facilitation and inhibition were observed in both reflexes (Fig. 3). The sequence could start with facilitation or inhibition. The latency of the initial effects was short (2.5 ms) indicating a minimum of two synapses in the descending path. The period of the rhythmic sequence was approximately 10 ms. Optimal parameters for the conditioning cortisol stimuli were found to be: trains of 3-5 surface anodal pulses, 0.5 ms, 400 Hz. The threshold of the cortical effects on the reflexes was 0.3 mA. A single pulse evoked effects. The cortical origin of the effects was located and related to the somatosensory projections, and to the cytoarchitecture. The effects of largest amplitude and most complex time course were evoked from the oral and perioral projections to areas 3a and 3b. Effects evoked from areas 4 gamma, 5a, and 6a beta were less complex and of lower amplitude. It is suggested that a trigemino-cortico-trigeminal loop via 3a may function in reflex modulation of the jaw movements. In addition area 3a may contribute to cortico-cortical motor elaborations via U-fiber connections to area 4 gamma.

The geology and mineral resources of Sierra Leone

Sierra Leone forms the central part of the sundered West African craton whose counterpart forms the Guyana Shield of northern South America. Three Archean to early Proterozoic thermotectonic events and the early Phanerozoic Pan-African orogeny preceded the breakup of the original craton in the early Jurassic by rift faulting and the intrusion of tholeiitic magmas to form new oceanic crust which accompanied the opening of the Atlantic ocean.The Archean rocks of Sierra Leone consist of a granitic basement containing elements of early sedimentary and mafic formations and a group of supracrustal greenstone belts with banded ironstone and detrital sediments. These are mineralized with gold, chromite, tin, copper, nickel, antimony, arsenic, and iron ores and are intruded by molybdenum-bearing granites. Lateritic weathering and alluviation has led to economic concentrations of diamonds, bauxite, and lateritic iron ores and to heavy mineral concentrates, particularly rutile. Prospects for lateritic nickel deposits appear to be good.Little exploration has been carried out in the poorly exposed Rokel River Group of late Proterozoic age. This formation and also the Ordovician (?) Saoinya Scarp Group contain glacial sediments in their lower horizons. The Triassic-Lower Jurassic Free-town Layered Basic Complex lies upon the continental margin and was formed by successive pulses of basic magma which formed a rhythmic sequence of troctolite, gabbro, and anorthosite which in some cases ended with an iron-enriched ilmenite-magnetite horizon and acid veining. Some alluvial platinum has been won from this complex, but the source rock has not yet been identified.Kimberlite dikes were emplaced in the Cretaceous period and have been the sources of the country's diamond mining industry. The Tertiary and Pleistocene sediments are known to contain horizons carrying lignite and ceramic clays and may also contain exploitable concentrations of other minerals.