Functional Organization of Auditory Cortex in the Mongolian Gerbil (Meriones unguiculatus) II. Tonotopic 2‐Deoxyglucose

Abstract

The tonotopic organization of the auditory cortex in the Mongolian gerbil was mapped with 2-deoxyfluoro-D-glucose (2DG) using narrow-band frequency-modulated tones of different centre frequency (FM tones) and tones periodically alternating between two different frequencies (alternating tones) as stimuli. Continuous tone bursts of a constant frequency and repetition rate were used in initial experiments. Continuous tones produced 2DG patterns similar to those observed in animals that were not specifically stimulated. With tone bursts of constant frequency and repetition rate variable patterns were observed, some of which could be interpreted only in retrospect in the light of results obtained with FM tones and alternating tones. These stimuli, in contrast, produced differential metabolic responses which in conjunction with 2DG data from monaural animals and electrophysiological data made it possible to distinguish a primary auditory field AI with its dorsal region Ald, an anterior auditory field AAF, a ventral field V, a dorsoposterior field DP and a ventroposterior field VP, a dorsal field D, and in addition an anteroventral field AV. In the largest field (AI) and the smaller rostrally adjacent field AAF, frequency-specific dorsoventral bands of labelling (isofrequency contours) were mapped quantitatively. Bands shifted as a function of frequency relative to each other and to an independent spatial reference line in the lateral hippocampus. Spatial analysis of the single bands obtained with FM tones, and of the double bands obtained with alternating tones in both fields, revealed roughly mirror-imaged tonotopic maps of AI and AAF. In AI the progression from low to high frequencies was from caudal to rostral and in AAF the gradient was reversed, leading to a common high-frequency border of the two fields. In AI, the spatial resolution for frequencies below 16 kHz was in similar intervals per octave and higher for frequencies below 1 kHz. AI showed a somewhat higher spatial resolution for frequencies (at least below 1 kHz) as well as longer isofrequency contours than AAF. The 2-deoxyglucose patterns provided average tonotopic maps and topological data on various fields, as well as reliable landmarks in the gerbil's auditory cortex.

Memory Consolidation for the Discrimination of Frequency-Modulated Tones in Mongolian Gerbils Is Sensitive to Protein-Synthesis Inhibitors Applied to the Auditory Cortex

“…Each injection yielded an injection track visible in the horizontal sections. Metric analysis confirmed the proper placement of the injection sites in the primary (AI), anterior (AAF), and posterior (DP/VP) fields of the auditory cortex (see Scheich et al 1993a;Budinger et al 2000a). A representative case is shown in Figure 1.…”

“…For each section its dorsoventral position is indicated as referenced to the dorsal tip of the corpus striatum (cf. Scheich et al 1993a). The injection tracks for each of the auditory cortical fields are marked by arrows connected with solid lines.…”

“…The injection tracks for each of the auditory cortical fields are marked by arrows connected with solid lines. The dashed line marks the rostrocaudal position of the anterior tip of the hippocampus along which sections were aligned and which provides a suitable anatomical landmark for referencing the position of the individual cortical fields (Scheich et al 1993a;Budinger et al 2000a) and the corresponding injection tracks. Other abbreviations: c.str.…”

Consequences of unilateral hearing loss: Cortical adjustment to unilateral deprivation

“…A rostral band marking the AAF, and a more caudal band marking AI were visible in each section (see Fig. 3; and Thomas et al, 1993;Scheich et al, 1993). Once AI and AAF were identified, a 50 × 50 μm window was used to sample the OD in cortical layer IV of each region (e.g., arrow in Fig 3).…”

One hundred million years of interhemispheric communication: the history of the corpus callosum

“…These bilateral cells are probably connected to the other hemisphere via the corpus callosum. In primary and secondary auditory areas of the rat, in which different tones are represented as stripes across the respective areas, callosal cells have been described to be segregated in relation to the tonotopic representation, although there are some discrepancies in the details of this array (22)(23)(24)(25)(26).…”