Ingrid S. Johnsrude

Cerebral asymmetry and the effects of sex and handedness on brain structure: a voxel-based morphometric analysis of 465 normal adult human brains.

We used voxel-based morphometry (VBM) to examine human brain asymmetry and the effects of sex and handedness on brain structure in 465 normal adults. We observed significant asymmetry of cerebral grey and white matter in the occipital, frontal, and temporal lobes (petalia), including Heschls gyrus, planum temporale (PT) and the hippocampal formation. Males demonstrated increased leftward asymmetry within Heschls gyrus and PT compared to females. There was no significant interaction between asymmetry and handedness and no main effect of handedness. There was a significant main effect of sex on brain morphology, even after accounting for the larger global volumes of grey and white matter in males. Females had increased grey matter volume adjacent to the depths of both central sulci and the left superior temporal sulcus, in right Heschls gyrus and PT, in right inferior frontal and frontomarginal gyri and in the cingulate gyrus. Females had significantly increased grey matter concentration extensively and relatively symmetrically in the cortical mantle, parahippocampal gyri, and in the banks of the cingulate and calcarine sulci. Males had increased grey matter volume bilaterally in the mesial temporal lobes, entorhinal and perirhinal cortex, and in the anterior lobes of the cerebellum, but no regions of increased grey matter concentration.

The problem of functional localization in the human brain.

Functional imaging gives us increasingly detailed information about the location of brain activity. To use this information, we need a clear conception of the meaning of location data. Here, we review methods for reporting location in functional imaging and discuss the problems that arise from the great variability in brain anatomy between individuals. These problems cause uncertainty in localization, which limits the effective resolution of functional imaging, especially for brain areas involved in higher cognitive function.

The Processing of Temporal Pitch and Melody Information in Auditory Cortex

An fMRI experiment was performed to identify the main stages of melody processing in the auditory pathway. Spectrally matched sounds that produce no pitch, fixed pitch, or melody were all found to activate Heschls gyrus (HG) and planum temporale (PT). Within this region, sounds with pitch produced more activation than those without pitch only in the lateral half of HG. When the pitch was varied to produce a melody, there was activation in regions beyond HG and PT, specifically in the superior temporal gyrus (STG) and planum polare (PP). The results support the view that there is hierarchy of pitch processing in which the center of activity moves anterolaterally away from primary auditory cortex as the processing of melodic sounds proceeds.

Identifying global anatomical differences: Deformation-based morphometry

The aim of this paper is to illustrate a method for identifying macroscopic anatomical differences among the brains of different populations of subjects. The method involves spatially normalizing the structural MR images of a number of subjects so that they all conform to the same stereotactic space. Multivariate statistics are then applied to the parameters describing the estimated nonlinear deformations that ensue. To illustrate the method, we compared the gross morphometry of male and female subjects. We also assessed brain asymmetry, the effect of handedness, and interactions among these effects. Hum. Brain Mapping 6:348–357, 1998.

Encoding of the temporal regularity of sound in the human brainstem

We measured the neural activity associated with the temporal structure of sound in the human auditory pathway from cochlear nucleus to cortex. The temporal structure includes regularities at the millisecond level and pitch sequences at the hundreds-of-milliseconds level. Functional magnetic resonance imaging (fMRI) of the whole brain with cardiac triggering allowed simultaneous observation of activity in the brainstem, thalamus and cerebrum. This work shows that the process of recoding temporal patterns into a more stable form begins as early as the cochlear nucleus and continues up to auditory cortex.

A common neural substrate for the analysis of pitch and duration pattern in segmented sound

The analysis of patterns of pitch and duration over time in natural segmented sounds is fundamentally relevant to the analysis of speech, environmental sounds and music. The neural basis for differences between the processing of pitch and duration sequences is not established. We carried out a PET activation study on nine right-handed musically naive subjects, in order to examine the basis for early pitch- and duration-sequence analysis. The input stimuli and output task were closely controlled. We demonstrated a strikingly similar bilateral neural network for both types of analysis. The network is right lateralised and includes the cerebellum, posterior superior temporal cortices, and inferior frontal cortices. These data are consistent with a common initial mechanism for the analysis of pitch and duration patterns within sequences.

Left-hemisphere specialization for the processing of acoustic transients.

PREVIOUS work suggests that speech sounds incorporating short-duration spectral changes (such as the formation transitions of stop consonants) rely on left hemisphere mechanisms for their adequate processing to a greater degree than do speech sounds incorporating spectral changes of a longer duration (such as vowel sounds). Ten normal subjects were scanned using positron emission tomography while discriminating pure tone stimuli incorporating frequency glides of either short or long duration. A comparison of these two conditions yielded significant activation foci in left orbitofrontal cortex, left fusiform gyrus, and right cerebellum. Because non-linguistic stimuli were used, these foci must reflect some basic low level aspect of neural processing that may be relevant to speech but cannot be a consequence of accessing the speech system itself.

Residual auditory function in persistent vegetative state: a combined pet and fmri study

In recent years, a number of studies have demonstrated an important role for functional neuroimaging in the identification of residual cognitive function in persistent vegetative state. Such studies, when successful, may be particularly useful where there is concern about the accuracy of the diagnosis and the possibility that residual cognitive function has remained undetected. Unfortunately, functional neuroimaging in persistent vegetative state is extremely complex and subject to numerous methodological, clinical and theoretical difficulties. Here, we describe the strategy used to study residual auditory and speech processing in a single patient with a clinical diagnosis of persistent vegetative state. Identical positron emission tomography studies, conducted nine months apart, revealed preserved and consistent responses in predicted regions of auditory cortex in response to intelligible speech stimuli. Moreover, a preliminary functional magnetic resonance imaging examination at the time of the second session revealed partially intact responses to semantically ambiguous stimuli, which are known to tap higher aspects of speech comprehension. In spite of the multiple logistic and procedural problems involved, these results have major clinical and theoretical implications and provide a strong basis for the systematic study of possible residual cognitive function in patients diagnosed as being in a persistent vegetative state.

Relationships between human auditory cortical structure and function

The human auditory cortex comprises multiple areas, largely distributed across the supratemporal plane, but the precise number and configuration of auditory areas and their functional significance have not yet been clearly established. In this paper, we discuss recent research concerning architectonic and functional organisation within the human auditory cortex, as well as architectonic and neurophysiological studies in non-human species, which can provide a broad conceptual framework for interpreting functional specialisation in humans. We review the pattern in human auditory cortex of the functional responses to various acoustic cues, such as frequency, pitch, sound level, temporal variation, motion and spatial location, and we discuss their correspondence to what is known about the organisation of the auditory cortex in other primates. There is some neuroimaging evidence of multiple tonotopically organised fields in humans and of functional specialisations of the fields in the processing of different sound features. It is thought that the primary area, on Heschl’s gyrus, may have a larger involvement in processing basic sound features, such as frequency and level, and that posterior non-primary areas on the planum temporale may play a larger role in processing more spectrotemporally complex sounds. Ways in which current knowledge of auditory cortical organisation and different data analysis approaches may benefit future functional neuroimaging studies which seek to link auditory cortical structure and function are discussed.

A cognitive activation study of memory for spatialrelationships

Twelve neurologically normal right-handed subjects were asked to remember the locations of eight representational drawings, presented one at a time, together with two landmarks (white squares), on a computer screen. Subjects were then scanned using positron emission tomography (PET) while performing forced-choice recognition of object location in four conditions, using either the original landmarks or two of the other objects as cues. In two conditions, the absolute location of the objects was unchanged from the time of encoding (fixed-array conditions), whereas in the other two, the location of the objects was shifted, although the spatial relationship among the objects and landmarks was maintained (shifted-array conditions). Subjects were also scanned in a control condition that made the same perceptual and motor demands as the recognition tasks but that had no mnemonic component. Compared to the control condition, all of the recognition tasks activated both the dorsal and ventral visual pathways bilaterally, but with notable asymmetries. In particular, activation in the right, but not left, inferior temporal gyrus (area 37) was observed when both shifted-array conditions were compared to their respective cue-matched fixed-array conditions. The recognition conditions with landmark cues were associated with focal increases in regional cerebral blood flow (rCBF) in the region of the right parahippocampal gyrus. The results support previous reports of involvement of the right mesial temporal region in object-location memory tasks, and suggest that right inferotemporal cortex is involved in extracting the invariant relational features of a visual scene.