Cortex

But in a tentative and schematic way, may collegues and I (Mishkin) can begin to describe how the brain remembers. Ultimately, to be sure, memory is a series of molecular events. What we chart is the territory within which those events take place. Measurements of the electrical activity of neurons or their uptake of radioactive glucose have distinguished parts of the brain that are active during tasks related to learning. With the increase in (brain) size has come greater complexity. The structures we study in the macaque all have counterparts in the human brain, but their functions may well have diverged in the course of evolution. A study of the neural pathway responsible for visual perception was in fact the starting point for our inquiry into memory. These results and others led us to postulate that visual information is processed sequentially along the path. The cells respond to progressively more of an object's physical properties including its size, shape, color and texture-until, in the final stations of the interferior temporal cortex, they synthesize a complete representation of the object.

A complex link exists between vision and unilateral spatial neglect (USN). Firstly, USN is not a perceptual deficit, secondly, USN is not necessarily accompanied by a visual deficit and finally, USN can be observed in non-visual modalities as well as in mental spatial imagery. This apparent supramodality of USN stands in sharp contrast to the fact that neglect signs are often more severe and more durable in the visual than in other sensory modalities (Chokron et al., 2002). The influence of vision on spatial representation has rarely been studied. In the present study we assessed six right brain-damaged patients suffering from left USN on two tasks involving spatial representations: a clock-drawing task and a drawing from memory task in two experimental conditions, with and without visual control. We confirm that even in mental imagery, the absence of visual feedback may decrease and even suppress left neglect signs (Bartolomeo and Chokron, 2001b; 2002). Since vision is largely involved in the orientation of attention in space, suppressing visual control could reduce the magnetic attraction towards the right ipsilesional hemispace and in this way could allow a re-orientation of attention towards the left neglected hemispace. We discuss the theoretical and therapeutic implications of these findings.

The visual mismatch negativity (vMMN) response is an event-related potential (ERP) component, which is automatically elicited by events that violate predictions based on prior events. VMMN experiments use visual stimulus repetition to induce predictions, and vMMN is obtained by subtracting the response to rare unpredicted stimuli from those to frequent stimuli. One increasingly popular interpretation of the mismatch response postulates that vMMN, similar to its auditory counterpart (aMMN), represents a prediction error response generated by cortical mechanisms forming probabilistic representations of sensory signals. Here we discuss the physiological and theoretical basis of vMMN and review thirty-three studies from the emerging field of its clinical applications, presenting a meta-analysis of findings in schizophrenia, mood disorders, substance abuse, neurodegenerative disorders, developmental disorders, deafness, panic disorder and hypertension. Furthermore, we include reports on ...

The exploitation of cassava tubers (Manihot utilissima) for various industrial, medicinal and food products requires the removal of the cortex, which is commonly carried out manually. Mechanization of this process has the potential of driving increased cultivation of cassava and generating products with high hygienic standard, product quality, processing efficiency, minimum loss of tubers and increased processing rate. The difficulty in achieving an acceptable peeling efficiency can be attributed to: the irregular shape of the tubers, the non uniformity of the cortex thickness and unavailability of technical data on parameters of design. This paper presents the solution to the cassava peeling problems and the development of a new machine capable of peeling cassava tubers with over 90 % efficiency. Cassava tubers have been classified according to their varieties. The varieties have been characterized. The relationship between tuber diameter and cortex thickness is established. These ...

Previous research has shown that word-to-picture matching for targets that cannot be named at pre-test results in improved naming relative to untreated control items for people with aphasia. This paper replicates and extends this finding and investigates its source. Is the effect a result of priming of semantic representations, or of post-semantic mechanisms in word retrieval?The first experiment shows that word-to-picture matching with unrelated distractors improves naming at short (2-3 minutes) and long (up to 25 minute) lags. There was no effect of being made aware of the relationship between word-to- picture matching and picture naming. People who have a semantic impairment improve only with a short lag between word-to-picture matching and naming. Participants with less semantic impairment show larger priming effects that are equal at short and long lags between word-to-picture matching and naming.The second experiment shows that the facilitation effect is just as large for word-to-picture matching with unrelated distractors as with semantically-related distractors. Furthermore, overall there was no difference between matching with coordinate items and with associated items.The results of these experiments show that facilitation of naming by word-to-picture matching in people with aphasia cannot be a result of the priming of semantic representations. Instead they are consistent with two effects: word-to-picture matching results in priming at a lemma level for aphasic people with a semantic impairment that is only found with a short lag between word-to-picture matching and naming. Word-to-picture matching causes priming of the lemma to output lexicon entry mapping that benefits participants with less semantic impairment that is evident at both a short and long lag between word-to-picture matching and naming. These findings fit well with previous research on repetition priming of naming with normal subjects.

Colour agnosia concerns the inability to recognise colours despite intact colour perception, semantic memory for colour information, and colour naming. Patients with selective colour agnosia have been described and the deficit is associated with left hemisphere damage. Here we report a case study of a 43-year-old man who was referred to us with a stroke in his right cerebellar hemisphere. During the standard assessment it transpired that he was unable to name coloured patches. Detailed assessment of his colour processing showed that he suffers from a selective colour agnosia. As he claimed to have had this problem all his life, and the fact that the infratentorial infarct that he had incurred was in an area far away from the brain structures that are known to be involved in colour processing, we suggest that he is the first reported case of developmental colour agnosia.

In this study, the effects of vigabatrin on spike-and-wave discharges (SWDs) were measured in WAG/Rij rats, an animal model of absence epilepsy. Vigabatrin was used with the aim of enhancing GABAergic neurotransmission, and in this way to investigate the role of this process in the properties of SWDs. The study was carried out both in the rat, in vivo, and also using a computational model, in order to test different mechanisms that may account for the changes in SWDs after vigabatrin. The model parameters, representing GABA levels, were changed according to the known, and assumed, mechanism of action of the drug. The results show that the computational model can most adequately simulate the data obtained in vivo on the assumption that the enhancement of GABAergic neurotransmission due to application of vigabatrin is most pronounced at the level of the thalamic relay nuclei (TC cells). Furthermore, vigabatrin was shown to affect both the SWD starting and stopping mechanisms, as refle...

Zoothamnium niveum (Hemprich & Ehrenberg, 1831) Ehrenberg, 1838, a colonial, sessile representative of the Peritrichida (Ciliophora, Oligohymenophora) from the mangrove channels of Twin Cays (Belize Barrier Reef, Caribbean Sea), is remarkable for an obligatory association with ectosymbiotic, chemoautotrophic bacteria. The ultrastructure of the host and the symbiont is investigated by means of low-temperature and conventional scanning electron microscopy, thin section and freeze-fracture transmission electron microscopy. The cortex, the main interface between host and symbiont, differs from the general pattern found in other peritrichs only in having special inclusions of unknown nature and function in the pellicular alveoli. The stationary microzooids and the swarming macrozooids have a fully developed oral ciliature, similar to other peritrichs. The cytopharynx in the macrozooids is highly reduced and no food vacuoles have been detected. Two morphotypes of bacteria, different in size and shape, are present on different parts of the colony and are assumed to represent only one species. The ultrastructural features resemble those of sulfur-oxidizing bacteria. The microzooids feed on bacteria whose size, shape, and ultrastructure is similar to their symbionts. This supports the assumption that Z. niveum gains at least part of its nutrition from chemoautotrophic bacteria.

Synaesthesia, a neurological condition affecting approximately .05% of the population, is characterised by anomalous sensory perception: a stimulus in one sensory modality triggers an automatic, instantaneous, consistent response in another modality (e.g., sound evokes colour) or in a different aspect of the same modality (e.g., black text evokes colour). As evidence was limited to case studies based on self-report, the existence of synaesthesia was regarded with scepticism until the development of the Test of Genuineness (TOG) in 1987, which measures the consistency of stimulus-response linkage: synaesthetes typically score between 70-90% range, whereas controls typically score between 20-38%. However, the TOG had only limited ability to quantify the characteristics of visual synaesthesia. In this study, the revised Test of Genuineness (TOG-R), utilising the Pantone-based Cambridge Synaesthesia Charts, was given to 26 synaesthetes and 23 controls. Results confirmed that the TOG-R is equally accurate in the diagnosis of synaesthesia; synaesthetes scored significantly (t47 = 16.01, p < .001) higher (mean = 71.3%, SEM = 1.4%) than controls (mean = 33%, SEM = 2.0%). The TOG-R provides greater precision in quantifying the closeness of colour matches and enables a more detailed analysis of visual synaesthesia. Synaesthetes were phenotyped into broad- and narrowband based on their overall responsiveness to auditory stimuli, with bandwidth determined primarily by responsiveness to non-word stimuli. They were further sub-phenotyped based on responses to sub-groups of stimuli into word-colour (WC) and music-colour (MC). Development of this instrument has important implications for the diagnosis and phenotyping of visual synaesthesia.