Few morphological differences have been identified so far that distinguish the human brain from the brains of our closest relatives, the apes. Comparative analyses of the spatial organization of cortical neurons, including minicolumns, can aid our understanding of the functionally relevant aspects of microcircuitry. We measured horizontal spacing distance and gray-level ratio in layer III of 4 regions of human and ape cortex in all 6 living hominoid species: frontal pole (Brodmann area [BA] 10), and primary motor (BA 4), primary somatosensory (BA 3), and primary visual cortex (BA 17). Our results identified significant differences between humans and apes in the frontal pole (BA 10). Within the human brain, there were also significant differences between the frontal pole and 2 of the 3 regions studied (BA 3 and BA 17). Differences between BA 10 and BA 4 were present but did not reach significance. These findings in combination with earlier findings on BA 44 and BA 45 suggest that human brain evolution was likely characterized by an increase in the number and width of minicolumns and the space available for interconnectivity between neurons in the frontal lobe, especially the prefrontal cortex.

The M-current (I M ), comprised of Kv7 channels, is a voltage-activated K ϩ conductance that plays a key role in the control of cell excitability. In hippocampal principal cells, I M controls action potential (AP) accommodation and contributes to the medium-duration afterhyperpolarization, but the role of I M in control of interneuron excitability remains unclear. Here, we investigated I M in hippocampal stratum oriens (SO) interneurons, both from wild-type and transgenic mice in which green fluorescent protein (GFP) was expressed in somatostatin-containing interneurons. Somatodendritic expression of Kv7.2 or Kv7.3 subunits was colocalized in a subset of GFPϩ SO interneurons, corresponding to oriens-lacunosum moleculare (O-LM) cells. Under voltage clamp (VC) conditions at Ϫ30 mV, the Kv7 channel antagonists linopirdine/XE-991 abolished the I M amplitude present during relaxation from Ϫ30 to Ϫ50 mV and reduced the holding current (I hold ). In addition, 0.5 mM tetraethylammonium reduced I M , suggesting that I M was composed of Kv7.2-containing channels. In contrast, the Kv7 channel opener retigabine increased I M amplitude and I hold . When strongly depolarized in VC, the linopirdine-sensitive outward current activated rapidly and comprised up to 20% of the total current. In current-clamp recordings from GFPϩ SO cells, linopirdine induced depolarization and increased AP frequency, whereas retigabine induced hyperpolarization and arrested firing. In multicompartment O-LM interneuron models that incorporated I M , somatodendritic placement of Kv7 channels best reproduced experimentally measured I M . The models suggest that Kv3-and Kv7-mediated channels both rapidly activate during single APs; however, Kv3 channels control rapid repolarization of the AP, whereas Kv7 channels primarily control the interspike interval.

Premature birth is highly prevalent and associated with neurodevelopmental delays and disorders. Adverse outcomes, particularly in children born before 32 weeks of gestation, have been attributed in large part to white matter injuries, often found in periventricular regions using conventional imaging. To date, tractography studies of white matter pathways in children and adolescents born preterm have evaluated only a limited number of tracts simultaneously. The current study compares diffusion properties along 18 major cerebral white matter pathways in children and adolescents born preterm (n = 27) and full term (n = 19), using diffusion magnetic resonance imaging and tractography. We found that compared to the full term group, the preterm group had significantly decreased FA in segments of the bilateral uncinate fasciculus and anterior segments of the right inferior fronto-occipital fasciculus. Additionally, the preterm group had significantly increased FA in segments of the right and left anterior thalamic radiations, posterior segments of the right inferior fronto-occipital fasciculus, and the right and left inferior longitudinal fasciculus. Increased FA in the preterm group was generally associated with decreased radial diffusivity. These findings indicate that prematurity-related white matter differences in later childhood and adolescence do not affect all tracts in the periventricular zone and can involve both decreased and increased FA. Differences in the patterns of radial diffusivity and axial diffusivity suggest that the tissue properties underlying group FA differences may vary within and across white matter tracts. Distinctive diffusion properties may relate to variations in the timing of injury in the neonatal period, extent of white matter dysmaturity and/or compensatory processes in childhood.

Anorexia nervosa (AN) is a serious eating disorder that typically emerges during adolescence and occurs most frequently in females. To date, very few studies have investigated the possible impact of AN on white matter tissue properties during adolescence, when white matter is still developing. The present study evaluated white matter tissue properties in adolescent girls with AN using diffusion MRI with tractography and T1 relaxometry to measure R1 (1/T1), an index of myelin content. Fifteen adolescent girls with AN (mean age = 16.6 years ± 1.4) were compared to fifteen age-matched girls with normal weight and eating behaviors (mean age = 17.1 years ± 1.3). We identified and segmented 9 bilateral cerebral tracts (18) and 8 callosal fiber tracts in each participant's brain (26 total). Tract profiles were generated by computing measures for fractional anisotropy (FA) and R1 along the trajectory of each tract. Compared to controls, FA in the AN group was significantly decreased in 4 of 26 white matter tracts and significantly increased in 2 of 26 white matter tracts. R1 was significantly decreased in the AN group compared to controls in 11 of 26 white matter tracts. Reduced FA in combination with reduced R1 suggests that the observed white matter differences in AN are likely due to reductions in myelin content. For the majority of tracts, group differences in FA and R1 did not occur within the same tract. The present findings have important implications for understanding the neurobiological factors underlying white matter changes associated with AN and invite further investigations examining associations between white matter properties and specific physiological, cognitive, social, or emotional functions affected in AN.

How the brain extracts words from auditory signals is an unanswered question. We recorded approximately 150 single and multi-units from the left anterior superior temporal gyrus of a patient during multiple auditory experiments. Against low background activity, 45% of units robustly fired to particular spoken words with little or no response to pure tones, noise-vocoded speech, or environmental sounds. Many units were tuned to complex but specific sets of phonemes, which were influenced by local context but invariant to speaker, and suppressed during self-produced speech. The firing of several units to specific visual letters was correlated with their response to the corresponding auditory phonemes, providing the first direct neural evidence for phonological recoding during reading. Maximal decoding of individual phonemes and words identities was attained using firing rates from approximately 5 neurons within 200 ms after word onset. Thus, neurons in human superior temporal gyrus use sparse spatially organized population encoding of complex acoustic-phonetic features to help recognize auditory and visual words.

Congenitally deaf individuals receive little or no auditory input, and when raised by deaf parents, they acquire sign as their native and primary language. We asked two questions regarding how the deaf brain in humans adapts to sensory deprivation: (1) Is meaning extracted and integrated from signs using the same classical left hemisphere fronto-temporal network used for speech in hearing individuals, and (2) in deafness, is superior temporal cortex encompassing primary and secondary auditory regions reorganized to receive and process visual sensory information at short latencies? Using magnetoencephalography (MEG) constrained by individual cortical anatomy obtained with magnetic resonance imaging (MRI), we examined an early time window associated with sensory processing and a late time window associated with lexico-semantic integration. We found that sign in deaf individuals and speech in hearing individuals activate a highly similar left fronto-temporal network (including superior temporal regions surrounding auditory cortex) during lexico-semantic processing, but only speech in hearing individuals activates auditory regions during sensory processing. Thus, neural systems dedicated to processing high-level linguistic information are utilized for processing language regardless of modality or hearing status, and we do not find evidence for re-wiring of afferent connections from visual systems to auditory cortex.

The present study quantitatively compared the basilar dendritic/spine systems of lamina V pyramidal neurons across four hierarchically arranged regions of neonatal human neocortex. Tissue blocks were removed from four Brodmann’s areas (BAs) in the left hemisphere of four neurologically normal neonates (mean age = 41 ± 40 days): primary (BA4 and BA3-1-2), unimodal (BA18), and supramodal cortices (BA10). Tissue was stained with a modified rapid Golgi technique. Ten cells per region (N = 160) were quantified. Despite the small sample size, significant differences in dendritic/spine extent obtained across cortical regions. Most apparent were substantial differences between BA4 and BA10: total dendritic length was 52% greater in BA4 than BA10, and dendritic spine number was 67% greater in BA4 than BA10. Neonatal patterns were compared to adult patterns, revealing that the relative regional pattern of dendritic complexity in the neonate was roughly the inverse of that established in the adult, with BA10 rather than BA4 being the most complex area in the adult. Overall, regional dendritic patterns suggest that the developmental time course of basilar dendritic systems is heterochronous and is more protracted for supramodal BA10 than for primary or unimodal regions (BA4, BA3-1-2, BA18).

Diffusion properties of white matter tracts have been associated with individual differences in reading. Individuals born preterm are at risk of injury to white matter. In this study we compared the associations between diffusion properties of white matter and reading skills in children and adolescents born full term and preterm. 45 participants, aged 9–17 years, included 26 preterms (born < 36 weeks' gestation) and 19 full-terms. Tract fractional anisotropy (FA) profiles were generated for five bilateral white matter tracts previously associated with reading: anterior superior longitudinal fasciculus (aSLF), arcuate fasciculus (Arc), corticospinal tract (CST), uncinate fasciculus (UF) and inferior longitudinal fasciculus (ILF). Mean scores on reading for the two groups were in the normal range and were not statistically different. In both groups, FA was associated with measures of single word reading and comprehension in the aSLF, AF, CST, and UF. However, correlations were negative in the full term group and positive in the preterm group. These results demonstrate variations in the neurobiology of reading in children born full term and preterm despite comparable reading skills. Findings suggest that efficient information exchange required for strong reading abilities may be accomplished via a different balance of neurobiological mechanisms in different groups of readers.