use strict;
use XML::Simple qw(XMLin);

my $data = XMLin( $xml, ForceArray => [qw(Author)]);

#use Data::Dumper;
#print Dumper($data);

foreach my $author (@{$data->{AuthorList}{Author}}) {
    print "$author->{ForeName} $author->{LastName}\n";
}
[download]

or

use strict;
use XML::Rules;

my $parser = XML::Rules->new(
    rules => [
        _default => 'content',
        Author => 'as array',
        AuthorList => sub { return Authors => $_[1]->{Author} },
        PubmedArticle => 'pass',
    ],
    stripspaces => 7,
);
my $data = $parser->parse( $xml);

use Data::Dumper;
print Dumper($data);

foreach my $author (@{$data->{Authors}}) {
    print "$author->{ForeName} $author->{LastName}\n";
}
[download]

The later is a bit more work, but lets you tweak the resulting datastructure to better fit your needs.