Per E. Roland

Activation by attention of the human reticular formation and thalamic intralaminar nuclei.

It has been known for over 45 years that electrical stimulation of the midbrain reticular formation and of the thalamic intralaminar nuclei of the brain alerts animals. However, lesions of these sectors fail to impair arousal and vigilance in some cases, making the role of the ascending activating reticular system controversial. Here, a positron emission tomographic study showed activation of the midbrain reticular formation and of thalamic intralaminar nuclei when human participants went from a relaxed awake state to an attention-demanding reaction-time task. These results confirm the role of these areas of the brain and brainstem in arousal and vigilance.

Asymmetry in the human motor cortex and handedness.

Handedness is one of the most obvious functional asymmetries, but its relation to an anatomical asymmetry of the hand representation area in the motor cortex has not been demonstrated. This would be a crucial test for the hypothesis of structure-function correlation in cortical motor organization. Using magnetic resonance morphometry, we show for the first time that the depth of the central sulcus is related to handedness. In right-handers, the left central sulcus is deeper than the right, and vice versa in left-handers. Macrostructural asymmetry is complemented by a microstructural left-larger-than-right asymmetry in neuropil volume (i.e., tissue compartment containing dendrites, axons, and synapses) in Brodmanns area 4. These asymmetries suggest that hand preference is associated with increased connectivity (demonstrated by an increased neuropil compartment in left area 4) and an increased intrasulcal surface of the precentral gyrus in the dominant hemisphere.

Learning of Sequential Finger Movements in Man: A Combined Kinematic and Positron Emission Tomography (PET) Study

The cerebral structures participating in learning of a manual skill were mapped with regional cerebral blood flow (rCBF) measurements and positron emission tomography in nine healthy volunteers. The task was a complicated right‐hand finger movement sequence. The subjects were examined at three stages: during initial practice of the finger movement sequence, in an advanced stage of learning, and after they had learnt the finger movement sequence. Quantitative evaluation of video tapes and electromyographic records of the right forearm and hand muscles demonstrated that the finger movements significantly accelerated and became more regular. Significant mean rCBF increases were induced in the left motor hand area, the left premotor cortex, the left supplementary motor area, the left sensory hand area, the left supplementary sensory area and the right anterior lobe of the cerebellum. During the learning process significant depressions of the mean rCBF occurred bilaterally in the superior parietal lobule, the anterior parietal cortex and the pars triangularis of the right inferior frontal cortex. The mean rCBF increases in these structures during the initial stage of learning were related to somatosensory feedback processing and internal language for the guidance of the finger movements. These activations disappeared when the subjects had learnt the finger movement sequence. Conversely, the mean rCBF significantly rose during the course of learning in the midsector of the putamen and globus pallidus on the left side. It is suggested that during the learning phase of this movement sequence, the basal ganglia were critically involved in the establishment of the final motor programme.

Olfactory Functions Are Mediated by Parallel and Hierarchical Processing

How the human brain processes the perception, discrimination, and recognition of odors has not been systematically explored. Cerebral activations were therefore studied with PET during five different olfactory tasks: monorhinal smelling of odorless air (AS), single odors (OS), discrimination of odor intensity (OD-i), discrimination of odor quality (OD-q), and odor recognition memory (OM). OS activated amygdala-piriform, orbitofrontal, insular, and cingulate cortices and right thalamus. OD-i and OD-q both engaged left insula and right cerebellum. OD-q also involved other areas, including right caudate and subiculum. OM did not activate the insula, but instead, the piriform cortex. With the exception of caudate and subiculum, it shared the remaining activations with the OD-q, and engaged, in addition, the temporal and parietal cortices. These findings indicate that olfactory functions are organized in a parallel and hierarchical manner.

Human Somatosensory Area 2: Observer-Independent Cytoarchitectonic Mapping, Interindividual Variability, and Population Map

We analyzed the topographical variability of human somatosensory area 2 in 10 postmortem brains. The brains were serially sectioned at 20 microm, and sections were stained for cell bodies. Area 2 was delineated with an observer-independent technique based on significant differences in the laminar densities of cell bodies. The sections were corrected with an MR scan of the same brain obtained before histological processing. Each brains histological volume and representation of area 2 was subsequently reconstructed in 3-D. We found that the borders of area 2 are topographically variable. The rostral border lies between the convexity of the postcentral gyrus and some millimeters deep in the rostral wall of the postcentral sulcus. The caudal border lies between the fundus of the postcentral sulcus and some millimeters above it in the rostral wall. In contrast to Brodmanns map, area 2 does not extend onto the mesial cortical surface or into the intraparietal sulcus. When the postcentral sulcus is interrupted by a gyral bridge, area 2 crosses this bridge and is not separated into two segments. After cytoarchitectonic analysis, the histological volumes were warped to the reference brain of a computerized atlas and superimposed. A population map was generated in 3-D space, which describes how many brains have a representation of area 2 in a particular voxel. This microstructurally defined population map can be used to demonstrate activations of area 2 in functional imaging studies and therefore help to further understand the role of area 2 in somatosensory processing.

Brain atlases - a new research tool

Conventional brain atlases are collections of micrographs or schematic drawings of brain sections from one or a few brains in which anatomical structures are identified, for example, nuclei, cortical areas and fibre tracts. Conventional brain maps have now been replaced with modern computer-based brain atlases. The structures in computerized atlases are deformable so as to fit the sizes and shapes of individual brains, and transform three-dimensional reconstructions or images of brains into a standard brain format. In order to make generalizations about localization of function and structure at both the macroscopical and microscopical level computerized brain atlases are needed. Computerized brain atlases are also used to compensate for the shrinkage and distortions during sectioning and embedding of post-mortem brains, to study structural-functional relationships in the human brain at both the macroscopical and microscopical level, and variations in gross morphology and microstructure of the human brain, and for establishing a three-dimensional human-brain database for all of the above and also for topographically defined data from the literature.

Smelling of Odorous Sex Hormone-like Compounds Causes Sex-Differentiated Hypothalamic Activations in Humans

The anatomical pathways for processing of odorous stimuli include the olfactory nerve projection to the olfactory bulb, the trigeminal nerve projection to somatosensory and insular cortex, and the projection from the accessory olfactory bulb to the hypothalamus. In the majority of tetrapods, the sex-specific effects of pheromones on reproductive behavior is mediated via the hypothalamic projection. However, the existence of this projection in humans has been regarded as improbable because humans lack a discernable accessory olfactory bulb. Here, we show that women smelling an androgen-like compound activate the hypothalamus, with the center of gravity in the preoptic and ventromedial nuclei. Men, in contrast, activate the hypothalamus (center of gravity in paraventricular and dorsomedial nuclei) when smelling an estrogen-like substance. This sex-dissociated hypothalamic activation suggests a potential physiological substrate for a sex-differentiated behavioral response in humans.

The engine of reason, the seat of the soul: P.M. Churchland Publisher: The MIT Press, 1995; ISBN: 0-262-10053-3; GB £19.95

For the uninitiated, there are two major tendencies in the modeling of human cognition. The older, tradtional school believes, in essence, that full human cognition can be modeled by dividing the world up into distinct entities -called _symbol s_-such as “dog”, “cat”, “run”, “bite”, “happy”, “tumbleweed”, a nd so on, and then manipulating this vast set of symbols by a very complex and very subtle set of rules. The opposing school claims that this system, while it might be good at concluding that Paris is the capital of France or that there must be blood flowing in the left-rear leg of a cow, can never capture the full measure -indeed, the esse nce -of human cognition. For them, the esse ntial features of cognition emerge from the combined effects of myriad, tiny actions far below the surface of consciousness. This is the camp to which Paul Churchland belongs. Now, let us turn to Churchland’s book, _The Engine of Reason, the Seat of the Soul _. It is a clearly written, easily understood presentation of some of the most important ideas and impressive contributions of connectionism. He leads the reader s tep by step through various kinds of “connectionist” networks, from the simple backpropagation networks developed in the ear ly 1980’s through the recurrent networks that were developed in response to problems that the simpler networks could not handle. He extrapolates from these networks to vastly larger, vastly more powerful networks that he believes will ultimately lead to a full simulation of human cognition. He describes a number of fascinating case s tudies, including Charles Rosenberg and Terry Sejnowski’s NETtalk, an early connectionist network that learned to pronounce English words. His excellent discussion of NETtalk accurately captures the excitement that this seminal program generated around 1986 when it first forced many traditional artificial intelli gence researchers to sit up and take connectionism seriously. Perhaps more than any other program in the field, NETtalk was responsible for the tremendous surge of interest in connectionism and in emergent (“bottom up”) models of cognition. The book includes a detailed and extremely interesting chapter on connectionist approachs to stereoscopic vision, detection of mines by submarines, pronounciation and, even, crab movement! Churchland carefully explains why recurrent networks, as opposed to simple backpropagation networks, must be used to process seque nces of events. There are chapters on brain dysfunction, consciousness (including some ground-breaking work by Rodolfo Llinas on neo-cortical oscill ations and the Crick-Koch hypothesis that these oscill ations may be the seat of consciousness), and potential technical uses of neural networks, including medical diagnosis. It all makes for truly fascinating reading. There are, however, a number of important problems with this book that cannot be ignored. To begin with, the book all too frequently reads like an “infomercial” for connectionism and “prototype vectors”. Infomercials, as everyone knows, contain a certain amount of truth wrapped in hyperbole and sold with evangelistic fervor. This is emphatically not what the neural network research program needs. When enthusiasm for an idea causes its proponents to intentionally downplay, overlook or conceal major diff iculties with it, the inevitable result is not only bad science, but a disill usioned public. The first page of the book is almost certainly the worst of all. Churchland writes:

Human brain atlas : For high-resolution functional and anatomical mapping

We present the new computerized Human Brain Atlas (HBA) for anatomical and functional mapping studies of the human brain. The HBA is based on many high‐resolution magnetic resonance images of normal subjects and provides continuous updating of the mean shape and position of anatomical structures of the human brain. The structures are transformable by linear and nonlinear global and local transformations applied anywhere in 3‐D pictures to fit the anatomical structures of individual brains, which, by reformatting, are transformed into a high‐resolution standard anatomical format. The power of the HBA to reduce anatomical variations was evaluated on a randomized selection of anatomical landmarks in brains of 27 young normal male volunteers who were different from those on whom the standard brain was selected. The HBA, even when based only on standard brain surface and central structures, reduced interindividual anatomical variance to the level of the variance in structure position between the right and left hemisphere in individual brains.

Sensory feedback to the cerebral cortex during voluntary movement in man

This article describes a series of experiments directed toward the following questions: (1) Do signals from musculotendinous receptors reach consciousness? (2) Does feed-forward information of muscular force and expected extent of voluntary movement exist? To answer these questions data from voluntary compression of springs and strain-gauge have been analysed in healthy young subjects and in patients with unilateral focal lesions of the cerebral hemispheres. By successive elimination of information from other sources it was possible to verify that receptors in muscles and tendons do signal movement magnitude and muscular tension to the cerebral cortex, and that this information does indeed reach consciousness. There also exists a feed-forward mechanism signalling parameters of voluntary contraction. However, it is unclear whether peripheral, subcortical, or intracortical loops are directly involved. Perception of signals of muscular tension is abolished by lesions of the contralateral cortex near the central sulcus. It is possible that there exist separate cortical projection areas for kinaesthetic signals from muscles and from joints.