We have discovered a "left-edge boundary tone" (LEBT) occurring in the first prosodic word of Swedish main clauses but not in subordinate clauses (Roll, 2006; cf. Myrberg, 2010). The complementizer att 'that' can introduce both main clauses and subordinate clauses, which would be temporarily ambiguous were it not for the LEBT. The presence or absence of a LEBT can therefore lead to garden path effects. For example, with no LEBT, listeners expect subordinate clause structure. If they instead hear a word order typical of main clauses, they have been lead down the garden path. Using ERP, reanalysis of the unexpected structure is reflected in a P600 effect (Roll, Horne, & Lindgren, 2009; 2011; Roll & Horne, 2011). Upon hearing that a LEBT is missing at the beginning of a clause, listeners strongly activate subordinate clause structure. This gives rise to a PrAN with its most likely sources in Broca's area (Söderström, Horne, Mannfolk, van Westen, & Roll, 2018).